Speaker apparatus and methods useful in conjunction therewith

ABSTRACT

An actuation system for generating a physical effect, the system comprising at least one array of translating elements each constrained to travel alternately back and forth along a respective axis, toward first and second extreme positions respectively, in response to activation of first and second forces respectively; and a controller operative to use the first and second forces to selectably latch at least one subset of said translating elements into the first and second extreme positions respectively.

REFERENCE TO CO-PENDING APPLICATIONS

This is a continuation application of application Ser. No. 14/293,381filed Jun. 2, 2014, which is a continuation application of applicationSer. No. 12/744,127 filed May 21, 2010. Priority is claimed from U.S.provisional application No. 60/996,513, entitled “Improved SpeakerApparatus And Methods Useful In Conjunction Therewith” and filed 21 Nov.2007.

Reference is hereby additionally made to the following co-pendingapplications: U.S. Provisional Application 60/802,126 filed 22 May 2006and entitled “Apparatus for Generating Pressure”, U.S. ProvisionalApplication 60/872,488 filed 4 Dec. 2006 and entitled “Volume Control”,U.S. Provisional Application 60/907,450 filed 2 Apr. 2007 and entitled“Apparatus for Generating Pressure and Methods of Manufacture Thereof”,U.S. Provisional Application 60/924,203 filed 3 May 2007 and entitled“Apparatus and Methods for Generating Pressure Waves”, U.S. ProvisionalApplication 60/996,513 filed 21 Nov. 2007 and entitled “Improved SpeakerApparatus and Methods Useful in Conjunction Therewith”,PCT/IL2007/000618 filed 21 May 2007 and entitled “Direct Digital SpeakerApparatus Having a Desired Directivity Pattern”, PCT/IL2007/000621 filed21 May 2007 and entitled “Volume and Tone Control in Direct DigitalSpeakers”, PCT/IL2007/000622 filed 21 May 2007 and entitled “Apparatusand Methods for Generating Pressure Waves”; PCT/IL2007/000623 filed 21May 2007 and entitled “Arrays of current bearing elements useful forgenerating pressure waves”; and PCT/IL2007/000624 filed 21 May 2007 andentitled “Apparatus for Generating Pressure and Methods of ManufactureThereof”.

FIELD OF THE INVENTION

The present invention relates generally to actuators and specificallyinter alia to speakers.

BACKGROUND OF THE INVENTION

The state of the art for actuators comprising an array of microactuators is believed to be represented by the following, all of whichare US patent documents unless otherwise indicated:

-   -   2002/0106093: The Abstract, FIGS. 1-42 and paragraphs 0009,        0023, and 0028 show electromagnetic radiation, actuators and        transducers and electrostatic devices.    -   U.S. Pat. No. 6,373,955: The Abstract and column 4, line        34-column 5, line 55 show an array of transducers.    -   JP 2001016675: The Abstract shows an array of acoustic output        transducers.    -   U.S. Pat. No. 6,963,654: The Abstract, FIGS. 1-3, 7-9 and column        7, line 41-column 8, line 54 show the transducer operation based        on an electromagnetic force.    -   U.S. Pat. No. 6,125,189: The Abstract; FIGS. 1-4 and column 4,        line 1-column 5, line 46, show an electro-acoustic transducing        unit including electrostatic driving.    -   WO 8400460: The Abstract shows an electromagnetic-acoustic        transducer having an array of magnets.    -   U.S. Pat. No. 4,337,379: The Abstract; column 3, lines 28-40,        and FIGS. 4, 9 show electromagnetic forces.    -   U.S. Pat. No. 4,515,997: The Abstract and column 4, lines 16-20,        show volume level.    -   U.S. Pat. No. 6,795,561: Column 7, lines 18-20, shows an array        of micro actuators.    -   U.S. Pat. No. 5,517,570: The Abstract shows mapping aural        phenomena to discrete, addressable sound pixels.    -   JP 57185790: The Abstract shows eliminating the need for a D/A        converter.    -   JP 51120710: The Abstract shows a digital speaker system which        does not require any D-A converter.    -   JP 09266599: The Abstract shows directly applying the digital        signal to a speaker.    -   U.S. Pat. No. 6,959,096: The Abstract and column 4, lines 50-63        show a plurality of transducers arranged within an array.

Methods for manufacturing polymer magnets are described in the followingpublications:

Lagorce, L. K. and M. G. Allen, “Magnetic and Mechanical Properties ofMicro-machined Strontium Ferrite/Polyimide Composites”, IEEE Journal ofMicro-electromechanical Systems, 6(4), December 1997; and

Lagorce, L. K., Brand, O. and M. G. Allen, “Magnetic micro actuatorsbased on polymer magnets”, IEEE Journal of Micro-electromechanicalSystems, 8(1), March 1999.

U.S. Pat. No. 4,337,379 to Nakaya describes a planar electrodynamicselectro-acoustic transducer including, in FIG. 4A, a coil-likestructure.

U.S. Pat. No. 6,963,654 to Sotme et al describes a diaphragm, flat-typeacoustic transducer and flat-type diaphragm. The Sotme system includes,in FIG. 7, a coil-like structure.

Semiconductor digital loudspeaker arrays are known, such as thosedescribed in United States Patent document 20010048123, U.S. Pat. No.6,403,995 to David Thomas, assigned to Texas Instruments and issued 11Jun. 2002, U.S. Pat. No. 4,194,095 to Sony, U.S. Pat. No. 4,515,997 toWalter Stinger, and Diamond Brett M., et al, “Digital soundreconstruction using array of CMOS-MEMS micro-speakers”, Transducers'03, The 12^(th) International Conference on Solid State Sensors,Actuators and Microsystems, Boston, Jun. 8-12, 2003; and such as BBE'sDS48 Digital Loudspeaker Management System.

YSP 1000 is an example of a phased array speaker manufactured by Yamaha.Acoustical waveguides are known and may be designed using the principlesdescribed in conventional texts on acoustics such as, for example,Encyclopedia of Acoustics by Malcolm J. Crocker, Wiley-Inter-science;Apr. 22, 1997; Fundamentals of Acoustics by Lawrence E. Kinsler; TheScience and Applications of Acoustics by Daniel R. Raichel; Principlesof Vibration and Sound by Thomas D. Rossing; and Foundations ofEngineering Acoustics by Frank J. Fahy.

The disclosures of all publications and patent documents mentioned inthe specification, and of the publications and patent documents citedtherein directly or indirectly, are hereby incorporated by reference.

SUMMARY OF THE INVENTION

Certain embodiments of the present invention seek to provide an improvedspeaker.

There is thus provided, in accordance with an embodiment of the presentinvention, an actuation method for generating a physical effect, atleast one attribute of which corresponds to at least one characteristicof a digital input signal sampled periodically in accordance with aclock, the method comprising providing at least one array of movingelements each constrained to travel alternately back and forth along arespective axis in response to an electromagnetic force operative uponthe array when the array is in the presence of an alternating magneticfield, initially bringing the array of moving elements into at least onelatching position and subsequently reducing the magnitude of theelectromagnetic force, selectively latching at least one subset of themoving elements in at least one latching position thereby to preventindividual moving elements from responding to the electromagnetic force,receiving the clock and, accordingly, controlling application of theelectromagnetic force to the array of moving elements, and receiving thedigital input signal and controlling the latching accordingly.

Further in accordance with an embodiment of the present invention, themagnitude of the electromagnetic force is reduced to zero once the arrayof moving elements has been brought into the at least one latchingposition.

Still further in accordance with an embodiment of the present invention,the magnitude of the electromagnetic force is reduced to a level greaterthan zero once the array of moving elements has been brought into the atleast one latching position.

Also provided, in accordance with another embodiment of the presentinvention, is actuator apparatus for generating a physical effect, atleast one attribute of which corresponds to at least one characteristicof a digital input signal sampled periodically in accordance with aclock, the apparatus comprising at least one actuator device, eachactuating device including an array of moving elements, wherein eachindividual moving element is responsive to alternating magnetic fieldsand is constrained to travel alternately back and forth along arespective axis responsive to an electromagnetic force operativethereupon when in the presence of an alternating magnetic field; atleast one latch operative to selectively latch at least one subset ofthe moving elements in at least one latching position thereby to preventthe individual moving elements from responding to the electromagneticforce; a magnetic field control system operative to receive the clockand, accordingly, to control application of the electromagnetic force tothe array of moving elements; and a latch controller operative toreceive the digital input signal and to control the at least one latchaccordingly wherein the magnetic field control system is operative toreduce the magnitude of the electromagnetic force once the array ofmoving elements has initially been brought into the at least onelatching position.

Further provided, in accordance with another embodiment of the presentinvention, is actuator apparatus for generating a physical effect, atleast one attribute of which corresponds to at least one characteristicof a digital input signal sampled periodically in accordance with aclock, the apparatus comprising at least one actuator device, eachactuating device including an array of moving elements, wherein eachindividual moving element is responsive to alternating magnetic fieldsand is constrained to travel alternately back and forth along arespective axis responsive to an electromagnetic force operative uponthe array when the array is in the presence of an alternating magneticfield; at least one latch operative to selectively latch at least onesubset of the moving elements in at least one latching position therebyto prevent the individual moving elements from responding to theelectromagnetic force; a magnetic field control system operative toreceive the clock and, accordingly, to control application of theelectromagnetic force to the array of moving elements; and a latchcontroller operative to receive the digital input signal and to controlthe at least one latch accordingly, wherein the array comprises a set ofmoving elements which has a surface configuration more complex than asingle plane.

Further in accordance with an embodiment of the present invention, thesurface configuration comprises a curved surface portion.

Still further in accordance with an embodiment of the present invention,the curved surface portion comprises a portion of a sphere.

Additionally in accordance with an embodiment of the present invention,the curved surface portion comprises a portion of a cylinder.

Also in accordance with an embodiment of the present invention, thesurface configuration comprises a plurality of planar portions.

Yet further in accordance with an embodiment of the present invention,the plurality of planar portions together form a piecewise planarportion.

Additionally in accordance with an embodiment of the present invention,the plurality of planar portions are stacked one on top of another.

Also provided, in accordance with an embodiment of the presentinvention, is actuator apparatus for generating a physical effect, atleast one attribute of which corresponds to at least one characteristicof a digital input signal sampled periodically in accordance with aclock, the apparatus comprising at least one actuator device, eachactuating device including an array of moving elements, wherein eachindividual moving element includes at least one magnet responsive toalternating magnetic fields and is constrained to travel alternatelyback and forth along a respective axis responsive to an electromagneticforce operative upon the array when the array is in the presence of analternating magnetic field; a magnetic field generator coiled aroundindividual moving elements in the array of moving elements so as togenerate the alternating magnetic field, the magnets in the movingelements being translatably disposed at specific horizontal locationsabove the coiled magnetic field generator; at least one ferromagneticelement disposed under the magnetic field generator and sticking upthrough the magnetic field generator at least at one horizontal locationdisposed below the magnets; at least one latch operative to selectivelylatch at least one subset of the moving elements in at least onelatching position thereby to prevent the individual moving elements fromresponding to the electromagnetic force; a magnetic field control systemoperative to receive the clock and, accordingly, to control applicationof the electromagnetic force to the array of moving elements; and alatch controller operative to receive the digital input signal and tocontrol the at least one latch accordingly.

Further in accordance with an embodiment of the present invention, theferromagnetic element comprises a planar portion on which are defined aplurality of apertured upstanding members, each of which upstandingmembers protrudes through the magnetic field generator at a horizontallocation disposed below a magnet included in an individual movingelement within the array of moving elements, each of the upstandingmembers defining an air passage through which sound waves, generated bythe individual moving element, may propagate.

Still further in accordance with an embodiment of the present invention,at least some of the upstanding members comprise truncated cones.

Also provided, in accordance with an embodiment of the presentinvention, is an actuation method for generating a physical effect, atleast one attribute of which corresponds to at least one characteristicof a digital input signal sampled periodically in accordance with aclock, the method comprising providing at least one array of movingelements each constrained to travel alternately back and forth along arespective axis in response to an electromagnetic force operative uponthe array when the array is in the presence of an alternating magneticfield; selectively latching at least one subset of the moving elementsin at least one latching position thereby to prevent individual movingelements from responding to the electromagnetic force; receiving theclock and, accordingly, controlling application of the electromagneticforce to the array of moving elements; and receiving the digital inputsignal and controlling the latching step accordingly wherein thelatching occurs in accordance with a timing pattern introducing delaysfor the moving elements in the array so as to achieve sound having apredetermined directivity pattern which differs from a naturaldirectivity pattern which would have occurred if all moving elements inthe array were to operate synchronously.

Still further in accordance with an embodiment of the present invention,the predetermined directivity pattern comprises a omni-directionalpattern defining a sphere having a center point and wherein the delaycomprises the following quotient for each moving element P in the array:

${{delay} = \frac{r_{2}}{c}},$where r₂=distance between the center point and moving element P and c isthe velocity of sound through the medium in which the speaker isoperating.

Additionally in accordance with an embodiment of the present invention,the predetermined directivity pattern comprises a cylindrical patterndefining a cylinder having a cylinder axis and wherein the delaycomprises the following quotient for each moving element P in the array:

${{delay} = \frac{r_{1}}{c}},$where r₁=distance between the cylinder axis and the pressure-producingelement P and c is the velocity of sound through the medium in which thespeaker is operating.

Additionally in accordance with an embodiment of the present invention,the predetermined directivity pattern comprises a uni-directionalpattern defining a beam having a planar wave front and a wavepropagation direction and wherein the delay comprises the followingquotient for each moving element P in the array:

${{delay} = \frac{r_{3}}{c}},$where r₃=distance between a pre-determined plane, lying behind thesurface of the pressure-producing elements and parallel to the planarwave front and normal to the wave propagation direction, and thepressure-producing element P and c is the velocity of sound through themedium in which the speaker is operating.

Yet further provided, in accordance with yet another embodiment of thepresent invention, is actuator apparatus for generating a physicaleffect, at least one attribute of which corresponds to at least onecharacteristic of a digital input signal sampled periodically inaccordance with a clock, the apparatus comprising at least one actuatordevice, each actuating device including a first array of movingelements, wherein each individual moving element is responsive toalternating magnetic fields and is constrained to travel alternatelyback and forth along a respective axis responsive to an electromagneticforce operative thereupon when in the presence of an alternatingmagnetic field; a waveguide guiding sound-waves generated by the arrayso as to achieve a desired directivity pattern; at least one latchoperative to selectively latch at least one subset of the movingelements in at least one latching position thereby to prevent theindividual moving elements from responding to the electromagnetic force;a magnetic field control system operative to receive the clock and,accordingly, to control application of the electromagnetic force to thearray of moving elements; and a latch controller operative to receivethe digital input signal and to control the at least one latchaccordingly, including temporally staggering motion of individual movingelements so as to achieve the desired directivity pattern by reducinginterference between moving elements.

Further in accordance with an embodiment of the present invention, thewaveguide intersects the array thereby to define a waveguide-arrayintersection and wherein the latch controller is operative to temporallystagger motion of individual moving elements in the array such thatindividual moving elements move in order of their respective distancesfrom the waveguide-array intersection.

Still further in accordance with an embodiment of the present invention,the waveguide comprises a second array of moving elements which togetherwith the first array serves as a waveguide for sound waves produced byboth arrays.

Also provided, in accordance with another embodiment of the presentinvention, is actuator apparatus for generating a physical effect, atleast one attribute of which corresponds to at least one characteristicof a digital input signal sampled periodically in accordance with aclock, the apparatus comprising at least one actuator device, eachactuating device including a first array of moving elements, whereineach individual moving element is responsive to alternating magneticfields and is constrained to travel alternately back and forth along arespective axis responsive to an electromagnetic force operativethereupon when in the presence of an alternating magnetic field; awaveguide comprising a second array of moving elements guidingsound-waves generated by the arrays so as to achieve a desireddirectivity pattern; at least one latch operative to selectively latchat least one subset of the moving elements in at least one latchingposition thereby to prevent the individual moving elements fromresponding to the electromagnetic force; a magnetic field control systemoperative to receive the clock and, accordingly, to control applicationof the electromagnetic force to the array of moving elements; and alatch controller operative to receive the digital input signal and tocontrol the at least one latch accordingly.

Additionally in accordance with an embodiment of the present invention,the waveguide intersects the array.

Further in accordance with an embodiment of the present invention, thewaveguide has a surface area and the array has a planar main surface andmost of the waveguide's surface area is parallel to the main surface.

Also provided, in accordance with another embodiment of the presentinvention, is actuator apparatus for generating a physical effect, atleast one attribute of which corresponds to at least one characteristicof a digital input signal sampled periodically in accordance with aclock, the apparatus comprising at least one actuator device, eachactuating device including an array of moving elements, wherein eachindividual moving element is responsive to alternating magnetic fieldsand is constrained to travel alternately back and forth along arespective axis responsive to an electromagnetic force operativethereupon when in the presence of an alternating magnetic field, therebyto define an amplitude of motion, the amplitude of motion being lessthan an amplitude value ∈ derived assuming (a) a desired total soundpressure level implying a desired pressure P produced by each movingelement and (b) an application-specific oscillation frequency f_(s) andusing the following conventional formula to derive the amplitude valuefrom the pressure P and the oscillation frequency:

$\begin{matrix}{P = \frac{\sqrt{2} \cdot \pi \cdot \rho \cdot S \cdot ɛ \cdot f_{s}^{2}}{2 \cdot R_{0}}} & (1)\end{matrix}$

where ρ is the medium density, S is the piston surface area, ∈ is themotion amplitude (peak to peak) of an individual moving element, and R₀is the distance from the source, at least one latch operative toselectively latch at least one subset of the moving elements in at leastone latching position thereby to prevent the individual moving elementsfrom responding to the electromagnetic force; a magnetic field controlsystem operative to receive the clock and, accordingly, to controlapplication of the electromagnetic force to the array of movingelements; and a latch controller operative to receive the digital inputsignal and to control the at least one latch accordingly.

Further in accordance with an embodiment of the present invention, theamplitude of motion is less than the amplitude value c.

Still further in accordance with an embodiment of the present invention,those moving elements closest to the intersection move first.

Also provided, in accordance with another embodiment of the presentinvention, is a method for employing actuator apparatus to generate aphysical effect, at least one attribute of which corresponds to at leastone characteristic of a digital input signal sampled periodically inaccordance with a clock, the method comprising providing actuatorapparatus comprising at least one actuator device, each actuating deviceincluding an array of moving elements, wherein each individual movingelement is responsive to alternating magnetic fields and is constrainedto travel alternately back and forth along a respective axis responsiveto an electromagnetic force operative thereupon when in the presence ofan alternating magnetic field, at least one latch operative toselectively latch at least one subset of the moving elements in at leastone latching position thereby to prevent the individual moving elementsfrom responding to the electromagnetic force, a magnetic field controlsystem operative to receive the clock and, accordingly, to controlapplication of the electromagnetic force to the array of movingelements; and a latch controller operative to receive the digital inputsignal and to control the at least one latch accordingly; generatingelectrostatic force between at least an individual one of the movingelements and the at least one latch, the individual moving elementhaving at least one moving element surface, the latch having at leastone latch surface facing the moving element surface; and providing adielectric layer and applying the dielectric layer to at least anindividual one of the surfaces. Said providing may also includeadditional treatment to at least partly prevent charge trapping in thedielectric layer.

Still further in accordance with an embodiment of the present invention,the electrostatic force is generated by applying voltage generated by avoltage supply having positive and negative poles, the providing andapplying comprises connecting the negative pole of the voltage supply tothe individual surface to which the dielectric layer has been applied,and connecting the positive pole to a surface facing the individualsurface.

Still further in accordance with an embodiment of the present invention,the providing and applying comprises connecting the positive pole of thevoltage supply to the individual surface to which the dielectric layerhas been applied, and connecting the negative pole to a surface facingthe individual surface.

Further in accordance with an embodiment of the present invention,charge trapping is prevented by coating the dielectric layer with a thinconductive layer.

Still further in accordance with an embodiment of the present invention,each moving element P in the array operates with a delay comprising thefollowing quotient:

${{delay} = \frac{d}{c}},$where d=distance between the intersection and the pressure-producingelement P and c is the velocity of sound through the medium in which theapparatus is operating.

Also provided in accordance with an embodiment of the present invention,is an actuation method for generating a physical effect, at least oneattribute of which corresponds to at least one characteristic of adigital input signal sampled periodically in accordance with a clock,the method comprising providing at least one array of moving elementseach constrained to travel alternately back and forth along a respectiveaxis in response to an electromagnetic force operative upon the arraywhen the array is in the presence of an alternating magnetic field,thereby to generate a sound wave, and a waveguide intersecting the atleast one array thereby to define an elongate array-waveguideintersection location, and operative to guide the sound wave to achievea pre-determined directivity pattern, selectively latching at least onesubset of the moving elements in at least one latching position therebyto prevent individual moving elements from responding to theelectromagnetic force; receiving the clock and, accordingly, controllingapplication of the electromagnetic force to the array of movingelements; and receiving the digital input signal and controlling thelatching accordingly, wherein the latching comprises repeatedlyselecting a current subset of moving elements to be latched into anindividual extreme position, including determining the size of thesubset and determining the members of the current subset by selectingfrom among those moving elements not currently in the individual extremeposition, a set of moving elements which are closest to the intersectionlocation.

Further in accordance with an embodiment of the present invention, a LUTis used to perform the repeated selection, the LUT storing, for eachposition within the array, an ordinal number associated with theposition and selected such that the distance of the position from theintersection location is a function of the position.

Still further in accordance with an embodiment of the present invention,the elongate intersection location defining a plurality of rows, intowhich the moving elements are partitioned, the rows being disposedparallel to the intersection location, and wherein the set of movingelements closest to the intersection location is selected, from amongall moving elements of a given closeness to the intersection location,by preferring those moving elements which are close to a mid-axisbisecting the rows.

Also provided, in accordance with an embodiment of the presentinvention, is an actuation method for generating a physical effect, themethod comprising providing at least one array of translating elementseach constrained to travel alternately back and forth along a respectiveaxis, toward first and second extreme positions respectively, inresponse to activation of first and second forces respectively; andusing the first and second forces to selectably latch at least onesubset of the translating elements into the first and second extremepositions respectively.

Further in accordance with an embodiment of the present invention, thefirst and second forces on each individual translating element aregenerated by at least one voltage applied between the individualtranslating element and at least one respective electrode relative towhich the translating element is traveling.

Still further in accordance with an embodiment of the present invention,at least one translating element is operative to initially approach thefirst extreme position; and is subsequently operative to travel,alternately, from the first extreme position to the second extremeposition, and from the second extreme position back to the first extremeposition.

Additionally in accordance with an embodiment of the present invention,while the individual translating element initially approaches the firstextreme position, the first force comprises an at least almostperiodical force having a first period and activated in accordance witha first temporal schedule and the second force is an at least almostperiodical force having a second period identical to the first period,the second force being activated during the second period in accordancewith a second temporal schedule which is identical to, but shifted byhalf a period relative to, the first temporal schedule.

Further in accordance with an embodiment of the present invention, thefirst temporal schedule includes a first half period interval and asecond half period interval and wherein, during the first half periodinterval, the first force is low in magnitude relative to its magnitudeduring the second half period interval.

Still further in accordance with an embodiment of the present invention,the voltage has a first magnitude as the individual translating elementleaves the second extreme position and begins to travel toward the firstextreme position and has a second magnitude, smaller than the firstmagnitude, once the translating element has already reached the firstextreme position and the voltage is merely serving to latch thetranslating element into the first extreme position.

Also provided, in accordance with an embodiment of the presentinvention, is multi-layer actuator apparatus comprising a first layer,at least a portion of which is conductive; at least one secondoperational layer, at least at portion of which is conductive, havingformed therewithin: a plurality of operational units actuated byapplying voltage between conductive portions of the first and secondlayers; and at least one cut-out portion isolating at least one subsetof the plurality of operational units from all operational units outsideof the subset other than a connecting channel which connects the subsetof the plurality of operational units to all operational units outsideof the subset, thereby to define a fuse.

Further in accordance with an embodiment of the present invention, thefirst force on each individual translating element is generated by afirst voltage applied between the individual translating element and afirst electrode disposed at the first extreme position and wherein thesecond force on each individual translating element is generated by asecond voltage applied between the individual translating element and asecond electrode disposed at the second extreme position.

Still further in accordance with an embodiment of the present invention,even when an individual translating element is neither latched to thefirst extreme position nor traveling toward it, the first voltage is notuniformly zero, thereby to expedite subsequent increase of the firstvoltage to a higher level when the individual translating elementembarks on travel toward the first extreme position.

Additionally in accordance with an embodiment of the present invention,during at least a portion of time in which at least one individualtranslating element is latched to the first extreme position, the secondvoltage is not less than the first voltage, thereby to expeditesubsequent increase of the second voltage to a higher level when theindividual translating element embarks on travel toward the secondextreme position.

Also provided, in accordance with an embodiment of the presentinvention, is a latch controller comprising electronic circuitry thattransfers electric charge from at least one first electrode at least onesecond electrode thus increasing the power efficiency of the system.

Still further in accordance with an embodiment of the present invention,the latch controller also comprises at least one charge storage devicecapable of receiving charge from at least one electrode.

Still further in accordance with an embodiment of the present invention,the charge storage device is capable of transferring charge to at leastone electrode.

Also provided, in accordance with an embodiment of the presentinvention, is an actuation system for generating a physical effect, thesystem comprising at least one array of translating elements eachconstrained to travel alternately back and forth along a respectiveaxis, toward first and second extreme positions respectively, inresponse to activation of first and second forces respectively; and acontroller operative to use the first and second forces to selectablylatch at least one subset of the translating elements into the first andsecond extreme positions respectively.

Further in accordance with an embodiment of the present invention, thesystem also comprises a first layer, at least a portion of which isconductive; and the array is formed within at least one secondoperational layer, at least a portion of which is conductive, havingformed therewithin a plurality of operational units, each including atleast one translating element and actuated by applying voltage betweenconductive portions of the first and second layers; and at least onecut-out portion isolating at least one subset of the plurality ofoperational units from all operational units outside of the subset otherthan a connecting channel which connects the subset of the plurality ofoperational units to all operational units outside of the subset,thereby to define a fuse.

Still further in accordance with an embodiment of the present invention,the first and second forces comprise electro-static forces.

Also provided, in accordance with an embodiment of the presentinvention, is an actuation system comprising at least one array ofelastically translating elements, each constrained to travel, inresponse to a force operative thereupon, along a respective axis, from afirst extreme position, to a second extreme position, thereby to definea first half of a temporal phase, and, upon reaching the second extremeposition, to return to the first extreme position, thereby to define asecond half of a temporal phase; and a latching device providing onlytwo operative states for each individual elastically translating elementfrom among the array of elastically translating elements: a first statein which the individual elastically translating element is latched intoonly one of the first and second extreme positions; and a second statein which the individual elastically translating element is free.

Further in accordance with an embodiment of the present invention, thesystem also comprises a first layer, at least a portion of which isconductive; and wherein the array is formed within at least one secondoperational layer, at least at portion of which is conductive, havingformed therewithin a plurality of operational units, each including atleast one translating element and actuated by applying voltage betweenconductive portions of the first and second layers; and at least onecut-out portion isolating at least one subset of the plurality ofoperational units from all operational units outside of the subset otherthan a connecting channel which connects the subset of the plurality ofoperational units to all operational units outside of the subset,thereby to define a fuse.

Further in accordance with an embodiment of the present invention, thesystem also comprises a controller operative to cause a force tooperate, during a time period including at least one temporal phase, onat least one pair of adjacent elastically translating elements includingfirst and second elastically translating elements, the force operatingalternately, with a delay of half a phase, on the first and secondelements.

Still further in accordance with an embodiment of the present invention,the controller is operative to cause an elastic force to operate on theat least one pair by unlatching the at least one pair.

Additionally in accordance with an embodiment of the present invention,at least one attribute of the physical effect corresponds to at leastone characteristic of a digital input signal sampled periodically inaccordance with a clock, and application of at least one force to thearray of translating elements is controlled at least partly according tothe clock and latching is controlled at least partly according to thedigital input signal.

Further in accordance with an embodiment of the present invention, theattribute comprises at least one of the following attributes: intensity;and pitch.

Still further in accordance with an embodiment of the present invention,the first and second forces on each individual translating element aregenerated by at least one voltage applied between the individualtranslating element and at least one respective electrode relative towhich the translating element is traveling.

Also provided, in accordance with an embodiment of the presentinvention, is a method for manufacturing an actuation system forgenerating a physical effect, the method comprising providing at leastone array of translating elements each constrained to travel alternatelyback and forth along a respective axis, toward first and second extremepositions respectively, in response to activation of first and secondforces respectively; and providing a controller operative to use thefirst and second forces to selectably latch at least one subset of thetranslating elements into the first and second extreme positionsrespectively.

Also provided, in accordance with an embodiment of the presentinvention, is a method for manufacturing an actuation system, the methodcomprising providing at least one array of elastically translatingelements, each constrained to travel, in response to a force operativethereupon, along a respective axis, from a first extreme position, to asecond extreme position, thereby to define a first half of a temporalphase, and, upon reaching the second extreme position, to return to thefirst extreme position, thereby to define a second half of a temporalphase; and providing a latching device providing only two operativestates for each individual elastically translating element from amongthe array of elastically translating elements: a first state in whichthe individual elastically translating element is latched into only oneof the first and second extreme positions; and a second state in whichthe individual elastically translating element is free.

Additionally provided, in accordance with an embodiment of the presentinvention, is a method for manufacturing multi-layer actuator apparatus,the method comprising providing a first layer, at least a portion ofwhich is conductive; and providing at least one second operationallayer, at least at portion of which is conductive, having formedtherewithin a plurality of operational units actuated by applyingvoltage between conductive portions of the first and second layers; andat least one cut-out portion isolating at least one subset of theplurality of operational units from all operational units outside of thesubset other than a connecting channel which connects the subset of theplurality of operational units to all operational units outside of thesubset, thereby to define a fuse.

Regarding terminology used herein:

Array: This term is intended to include any set of moving elements whoseaxes are preferably disposed in mutually parallel orientation and flushwith one another so as to define a surface which may be planar orcurved.

Above, Below: It is appreciated that the terms “above” and “below” andthe like are used herein assuming that, as illustrated by way ofexample, the direction of motion of the moving elements is up and downhowever this need not be the case and alternatively the moving elementsmay move along any desired axis such as a horizontal axis.

Actuator: This term is intended to include transducers and other devicesfor inter-conversion of energy forms. When the term transducers is used,this is merely by way of example and it is intended to refer to allsuitable actuators such as speakers, including loudspeakers.

Actuator element: This term is intended to include any “column” ofcomponents which, typically in conjunction with many other such columns,forms an actuator, each column typically including a moving element, apair of latches or “latching elements” therefore, each latching elementincluding one or more electrodes and insulative spacing materialseparating the moving element from the latches.

Coil: It is appreciated that the alternating electromagnetic forceapplied to the array of moving elements in accordance with certainembodiments of the present invention may be generated by an alternatingelectric current oriented to produce a magnetic field gradient which isco-linear to the desired axes of motion of the moving elements. Thiselectric current may comprise current flowing through a suitablyoriented conductive coil or conductive element of any other suitableconfiguration. The term “coil” is used throughout the presentspecification as an example however it is appreciated that there is nointention to limit the invention which is intended to include allapparatus for applying an alternating electromagnetic force e.g. asdescribed above. When “coil” is used to indicate a conductor, it isappreciated that the conductor may have any suitable configuration suchas a circle or other closed figure or substantial portion thereof and isnot intended to be limited to configurations having multiple turns.

Channels, also termed “holes” or “tunnels”: Although these areillustrated as being cylindrical merely by way of example, this need notbe the case.

Electrode: An electro-static latch. Includes either the bottom or topelectro-static latch which latches its corresponding moving element byvirtue of its being oppositely charged such that each latch and itsmoving element constitute a pair of oppositely charged electrodes.

Flexure: at least one flexible element on which an object is mounted,imparting at least one degree of freedom of motion to that object, forexample, one or more flexible thin or small elements peripheral to andtypically integrally formed e.g. from a single sheet of material, with acentral portion on which another object may or may not be mounted,thereby to impart at least one degree of freedom of motion to thecentral portion and objects mounted thereupon.

Latch, latching layer, latching mechanism: This term is intended toinclude any device for selectively locking one or more moving elementsinto a fixed position. Typically, “top” and “bottom” latching layers areprovided, which may be side by side and need not be one atop the other,and each latching layer includes one or many latching mechanisms whichmay or may not correspond in number to the number of moving elements tobe latched. The term “latch pair” is a pair of latches for an individualmoving element e.g. including a top latch and a bottom latch, which maybe side by side and need not be one atop the other.

Moving elements: These are intended to include any moving elements eachconstrained to travel alternately back and forth along an axis inresponse to an alternating electromagnetic force applied thereto. Movingelements are also termed herein “micro-speakers”, “pixels”,“micro-actuators”, “membranes” (individually or collectively) and“pistons”.

Spacers, also termed “space maintainers”: Include any element orelements mechanically maintaining the respective positions of theelectrodes and moving elements. The term “direct digital speaker” isused herein to include speakers that accept a digital signal andtranslate the signal into sound waves without the use of a separatedigital to analog converter. Such speakers may sometimes include ananalog to digital converter as to allow them to translate analog signalsinstead or in addition to digital signals. Such speakers may include DDS(Direct Digital Speakers), DDL (Direct Digital Loudspeakers), DSR(Digital Sound Reconstruction) speakers, digital uniform loudspeakerarrays, matrix speakers, and MEMS speakers. The term “direct digitalspeaker” as used herein is intended to include speaker apparatus havinga multiplicity of pressure-producing elements, which generate pressureeither by virtue of their motion e.g. as specifically described hereinor by heating and cooling the medium in which they reside, e.g. air, orby accelerating the medium in which they reside e.g. by ionizing themedium and providing a potential difference along an axis, or byoperating as valves to selectively tap reservoirs of medium e.g. air,pressurized differently from the surrounding environment. The number ofoperating pressure producing elements (i.e. elements which are operatingto generate pressure) is typically a monotonically increasing functionof, e.g. proportional to the intensity of the input signal, if analog,or to the digitally encoded intensity of the input signal, if digital.

The term “clock” used herein refers to the time duration associated witha single interval of the system clock.

The term “directivity pattern” as used herein refers to the pattern ofthe spatial distribution of the acoustic energy generated by speakerapparatus.

BRIEF DESCRIPTION OF THE DRAWINGS

Certain embodiments of the present invention are illustrated in thefollowing drawings:

FIG. 1 shows graphs of system timing according to an embodiment in whichpower down of the magnetic field generator is provided after completionof the initialization sequence illustrated in FIG. 17D.

FIG. 2 shows graphs of system timing according to an embodiment in whichpower off is provided of the magnetic field generator after completionof the initialization sequence described in FIG. 17D.

FIGS. 3A-3D are examples of moving element array configurationsconstructed and operative in accordance with certain embodiments of thepresent invention.

FIG. 4 is a perspective view of an improved coil layer apparatus havinga ferromagnetic element protruding through a magnetic field generatorcoiled about the moving elements in accordance with certain embodimentsof the invention.

FIG. 5A is an enlarged view of a detail of FIG. 4.

FIG. 5B is a cross-sectional view of the apparatus of FIG. 4, alsoshowing magnets.

FIG. 6 illustrates an array of moving elements having a circular segmentconfiguration which may be used, in conjunction with a suitable temporalschedule for moving element operation, to generate an omni-directionalsynthetic directivity pattern having a radius which differs from theradius of the circular segment.

FIGS. 7A and 7B are cross-sectional and isometric illustrations,respectively, of an array of moving elements having a cylindricalsegment configuration which may be used, in conjunction with a suitabletemporal schedule for moving element operation, to generate acylindrical synthetic directivity pattern having a radius which differsfrom the radius of the cylindrical segment.

FIG. 8 is an isometric illustration of an array of moving elementshaving an arbitrary configuration which may be used, in conjunction witha suitable temporal schedule for moving element operation, to generate avariety of directivity patterns which differ from the naturaldirectivity pattern of the array.

FIGS. 9A and 9B are isometric and cross-sectional illustrations,respectively, of an array of moving elements and associated waveguide,constructed and operative in accordance with a first embodiment of thepresent invention.

FIG. 10A is a cross-sectional illustration of an array of movingelements and associated waveguide, constructed and operative inaccordance with a second embodiment of the present invention.

FIG. 10B is a cross-sectional illustration of an array of movingelements and associated waveguide, constructed and operative inaccordance with a third embodiment of the present invention.

FIG. 10C is an isometric illustration of a pair of arrays of movingelements together serving also as a waveguide, constructed and operativein accordance with a fourth embodiment of the present invention.

FIG. 11 is an example of a look-up table useful in performing the movingelement determination step in the flowchart of FIG. 21, for speakersconstructed and operative in accordance with an embodiment of thepresent invention which include a waveguide.

FIGS. 12A-12C are matrices useful in constructing LUTs for speakerswhich include a waveguide.

FIG. 13 is a simplified functional block diagram illustration ofactuator apparatus constructed and operative in accordance with certainembodiments of the present invention.

FIG. 14 is an isometric view of a skewed array of moving elements eachconstrained to travel alternately back and forth along a respective axisin response to an alternating electromagnetic force applied to the arrayof moving elements by a coil wrapped around the array.

FIG. 15 is an exploded view of an actuator device including an array ofmoving elements each constrained to travel alternately back and forthalong a respective axis in response to an alternating electromagneticforce applied to the array of moving elements by a coil, and a latch,formed as a layer, operative to selectively latch at least one subset ofthe moving elements in at least one latching position thereby to preventthe individual moving elements from responding to the electromagneticforce.

FIG. 16 is a simplified flowchart illustration of a suitable actuationmethod operative in accordance with certain embodiments of the presentinvention.

FIG. 17A is a control diagram illustrating control of the latches and ofthe coil-induced electromagnetic force for a particular example in whichthe moving elements are arranged in groups that can each, selectively,be actuated collectively, wherein each latch in the latching layer isassociated with a permanent magnet, and wherein the poles of all of thepermanent magnets in the latching layer are all identically disposed.

FIG. 17B is a flowchart illustrating a suitable method whereby alatching controller may process an incoming input signal and controlmoving elements' latches accordingly, in groups.

FIG. 17C is a simplified functional block diagram illustration of aprocessor, such as the processor 802 of FIG. 17A, which is useful incontrolling substantially any of the actuator devices with electrostaticlatch mechanisms shown and described herein.

FIG. 17D is a simplified flowchart illustration of a suitable method forinitializing the apparatus of FIGS. 13-17C.

FIG. 18A is a graph summarizing certain, although typically not all, ofthe forces brought to bear on moving elements in accordance with certainembodiments of the present invention.

FIG. 18B is a simplified pictorial illustration of a magnetic fieldgradient inducing layer constructed and operative in accordance withcertain embodiments of the present invention.

FIGS. 18C-18D illustrate the magnetic field gradient induction functionof the conductive layer of FIG. 18B.

FIG. 19 is an isometric array of actuators supported within a supportframe providing an active area which is the sum of the active areas ofthe individual actuator arrays.

FIG. 20A is a simplified generally self-explanatory functional blockdiagram illustration of a suitable system for achieving a desireddirectivity pattern for a desired sound stream using a direct digitalspeaker with characteristics as indicated in FIG. 20A e.g. that shownand described herein in FIGS. 13-19.

FIG. 20B is a simplified generally self-explanatory functional blockdiagram illustration of a suitable system for achieving a desireddirectivity pattern for a desired sound stream which is of generalapplicability in that it need not employ a direct digital speaker withcharacteristics as indicated in FIG. 20A e.g. that shown and describedherein in FIGS. 13-19 and may instead employ any suitable direct digitalspeaker.

FIG. 21 is a simplified flowchart illustration of per-clock operation ofthe moving element constraint controller 3050 of FIG. 20, in accordancewith certain embodiments of the present invention.

FIG. 22A is a simplified diagram of an omni-directional propagationpattern. FIG. 22B is a diagram of a suitable positioning of a movingelement array relative to the focal point of the desiredomni-directional sound propagation pattern of FIG. 22A.

FIG. 23A is an isometric view of small-stroke actuator apparatus,constructed and operative in accordance with certain embodiments of thepresent invention and having translating elements which requires noelectromagnetic force for its operation because electrostatic forces areemployed both to generate motion of the translating elements and tolatch them.

FIG. 23B is an exploded view of the apparatus of FIG. 23A.

FIG. 23C is an enlarged illustration of the bubble of FIG. 23A.

FIG. 24A is a simplified composite graph illustration of a suitabledisplacement (top graph) of a translating element in the actuatorapparatus of FIG. 23A and of voltage patterns which if applied to thetop (middle graph) and bottom (bottom graph) electrode layers of theactuator apparatus respectively, result in the desired displacementshown in the top graph, all in accordance with certain embodiments ofthe present invention.

FIG. 24B is a detailed graph illustration of voltages applied to the top(top graph) and bottom (bottom graph) electrode layers of the actuatorapparatus, during the “start procedure” phase shown in FIG. 24A in whichtranslating elements are put into motion, all according to certainembodiments of the present invention in which the “roof” of the pulsesis not flat but rather inclines upward and then downward e.g. as shown.

FIG. 24C is a detailed graph illustration of voltages applied to the top(top graph) and bottom (bottom graph) electrode layers of the actuatorapparatus, during the “up-down translation” and “down-up translation”phases shown in FIG. 24A, all according to certain embodiments of thepresent invention.

FIG. 25 is a simplified pictorial diagram of actuator apparatus havingonly one latch to latch its translating elements, the apparatus beingconstructed and operative in accordance with certain embodiments of thepresent invention.

FIG. 26 is a composite graph illustration of the velocity (solid line)and displacement (dashed line) for a cooperating pair of subsets oftranslating elements in the actuator apparatus of FIG. 25, according tocertain embodiments of the present invention, for an embodiment in whicha command to generate negative total pressure pulse is received when afirst subset of translating elements is close to the latching electrodeand is latched following the command, while the second subset oftranslating elements continues to move.

FIG. 27 is a composite graph illustration of the velocity (solid line)and displacement (dashed line) for a cooperating pair of translatingelements in the actuator apparatus of FIG. 25, according to certainembodiments of the present invention, for an embodiment in which acommand to generate negative total pressure pulse is received when asecond subset of translating elements is close to the latching electrodeand is latched following the command while the first subset oftranslating elements continues to move.

FIGS. 28A and 28B are isometric illustrations of the actuator apparatusof FIG. 25, constructed and operative in accordance with certainembodiments of the present invention.

FIGS. 29A and 29B are exploded illustrations of the actuator apparatusof FIGS. 28A and 28B respectively.

FIG. 30 is a diagram of an array of translating elements to be used, inpairs, to generate a sound.

FIG. 31 is a pressure vs. time graph for a sound to be generated usingthe array of FIG. 30 and using a scheme in which the controllerselectably latches (or not) all of the translating elements in the arrayinto a single extreme position e.g. the first extreme position, asopposed to schemes in which the controller selectably latches (or not)some of the translating elements into the first extreme position andothers of the translating elements into the second extreme position.

FIG. 32 is a composite graph including graphs of translations of each ofthe elements in the array of FIG. 30, as a function of time, suchtranslations being able to yield the sound depicted in FIG. 31.

FIG. 33 is a top cross-sectional illustration of actuator apparatusincluding a plurality of translating elements formed from a layer ofsuitable conductive material such as silicon, each having a fuse elementcomprising an isthmus of silicon, all constructed and operative inaccordance with certain embodiments of the present invention.

DETAILED DESCRIPTION OF CERTAIN EMBODIMENTS

According to certain embodiments of the invention, power may beconserved by turning off, or reducing the current through, theelectro-magnetic field generator at a suitable point in time e.g. aftercompletion of an initialization sequence provided in accordance withcertain embodiments of the present invention and described below withreference to FIG. 17D. The electro-magnetic field generator is typicallyturned off, or the current therethrough reduced, at the point where allmoving elements have been latched into one of their typically twoextreme positions, typically half of the moving elements being latchedinto each of the two positions. This is possible since the systemoperates in resonance and has a high Q factor such that theelectro-magnetic field is typically not necessary or hardly necessary inorder to ensure that the moving element is latched into a new, oppositeextreme position each time it is released.

FIG. 1 illustrates system timing graphs including a graph A depictingthe system clock, a graph B depicting a suitable power graph for theelectro-magnetic field generator, graph C depicting the verticaldisplacement of an individual moving element assuming the power graph ofB, assuming that the moving element is moving into a top latchingposition, and assuming that after approximately 6.5 millisec, the movingelement is released from its top latching position at which point itbegins to move toward its bottom latching position. Graphs D and Edepict the voltage levels of the top and bottom latches respectively. Asis apparent especially from Graph C, due to resonance, the amplitude ofthe moving element's periodic motion increases over time until, afterapproximately 4.5 millisec, it reaches an amplitude sufficient for it tobe electro-statically latched into its top latching position. After asuitable interval such as 0.5 millisec, the electro-magnetic fieldgenerator can be powered down as shown in FIG. 1, or even powered off asshown in FIG. 2. Typically, the powering-down or -off is compensated byincreasing the latching voltage. The increase in latching voltage anddecrease in electro-magnetic generator power may be selected to as tominimize power while still enabling latching to take place.

FIG. 2 is similar to FIG. 1 except that the electro-magnetic fieldgenerator is powered off rather than being powered down as in FIG. 1. Asis apparent by comparing Graphs D and E in FIGS. 1 and 2, the fact thatthe generator is powered off rather than down is compensated for byslightly increasing the latching voltage, e.g., in the illustratedexample, V₁ shown in FIG. 1 is lower than V₂ shown in FIG. 2.

As described above, according to certain embodiments, a set of movingelements is provided whose axes are typically substantially parallel andflush with one another so as to define a surface which may or may not beplanar. Each moving element is associated with other components such aslatches, coils and spacer layers, together forming a column. FIGS. 3A-3Dillustrate four exemplary sets of columns respectively, only the topsurfaces 2200 of which are visible. As shown, in FIG. 3A, the surfaces2200 define a main surface 2210 curved along two axes which may forexample comprise a portion of a spherical surface defined about a centerpoint 2215 and having a radius R. In FIG. 3B, the surfaces 2200 define amain surface 2220 curved about a single axis 2225; the main surface mayfor example comprise a portion of a cylindrical surface. In FIG. 3C, thesurfaces 2200 define a main surface 2230 which is piecewise planar inthat it comprises a plurality of connected planes (three planes, 2240,2250 and 2260, in the illustrated example). In FIG. 3D the surfaces 2200define a plurality of stacked surfaces (5 surfaces 2270, 2280, 2290,2300 and 2310 in the illustrated example). Since the columns inobstructed surfaces or portions of surfaces are effectively inoperative,the stacked surfaces typically are of sequentially diminishing sizes asshown. It is appreciated that the obstructed portions of the surfacesother than the top surface 2310 may or may not be formed with actualcolumns, so, for example, the columns in portion 2320 of bottom surface2270 may be omitted.

The configurations of FIGS. 3A-3D generate a respective variety ofdirectivity characteristics. For example, the configuration of FIG. 3Agenerates omni-directional directivity. More specifically, if the topsurfaces 2200 of the columns were to define a complete sphericalsurface, the directivity achieved would be wholly omni-directional; ifthe top surfaces define only a portion of the spherical surface asshown, the directivity achieved is partial i.e. a corresponding portionof omni-directionality is achieved. Specifically, good performance isachieved, other than fade, in a “natural good performance area”comprising a portion of the imaginary sphere delineated by the mainsurface 2210 and the set of radii connecting the perimeter of the mainsurface 2210 to the center 2215. It is appreciated that it is possibleto achieve, by employing suitable temporal staggering of the operationof the moving elements, good performance even outside the “natural goodperformance area”. For example, if it may be desired to achieve goodperformance in a “synthetic good performance area” comprising a portionof an imaginary sphere delineated by the main surface 2210 and the setof line segments connecting the main surface 2210 to an imaginary point2216, different from the real center 2215 of the main surface. It isfurther appreciated that it is possible to achieve, by employingsuitable temporal staggering of the operation of the moving elements,good performance at an area smaller than the “natural good performancearea”, by placing the imaginary point 2216 at a distance from thesurface 2210 which exceeds the distance of the real center 2215 from thesurface 2210.

Similarly, the configuration of FIG. 3B generates cylindricaldirectivity. More specifically, if the top surfaces 2200 of the columnswere to define a complete cylindrical surface, the directivity achievedwould be wholly cylindrical, i.e. a “natural good performance area”would be achieved, other than fade, in an area located in-between thetwo planes that form the top and bottom of the cylinder; if the surfaces2220 define only a portion of the cylindrical surface as shown, thedirectivity achieved is partial i.e. a corresponding portion ofcylindrical directionality is achieved. Specifically, good performanceis achieved, other than fade, in a “natural good performance area”comprising a portion of the imaginary cylinder delineated by the mainsurface 2220 and the set of normals connecting the perimeter of the mainsurface 2210 to the axis 2225. It is appreciated that it is possible toachieve, by suitable temporal staggering of the operation of the movingelements, good performance in an area larger or smaller than the“natural good performance area” of the portion-cylindrical array of FIG.3B. For example, it may be desired to achieve good performance in a“synthetic good performance area” comprising a portion of an imaginarycylinder delineated by the main surface 2220 and the set of shortestline segments connecting the main surface 2210 to an imaginary axis,different from the real axis 2225.

Referring again to FIG. 3B, if the axis 2225 is vertical then thedirectivity generated is horizontal, wholly or partially, hence suitablefor applications in which it is desired to generate sound only at aspecific vertical location e.g. within a certain floor in a multi-levelfacility. The configuration of FIGS. 3C and 3D are respectively similarto FIG. 3B in effect however are easier to manufacture and/or strongerin certain applications.

FIG. 4 is a perspective view of an improved coil layer apparatus 2400;FIG. 5A is a detail of FIG. 4 as indicated by bubble 2405. FIG. 5B is across-section of the apparatus of FIG. 5A also showing magnets 2407translatably disposed at specific horizontal locations above the coillayer. In the embodiment of FIGS. 4-5B, at least one magnetic fieldconductor layer 2410 formed e.g. of a ferromagnetic material isprovided, preferably disposed under the coil 2400 and also sticking upthrough the coil at least at the horizontal locations disposed below themagnets 2407. For example, in the illustrated embodiment, theferro-magnetic layer 2410 may comprise a planar portion 2415 in which isdefined an array of apertured upstanding members 2420 such as aperturedtruncated cones 2420 disposed under each magnet 2407. Each upstandingmember 2420 defines an air passage 2430 through which sound wavesgenerated by the moving elements associated with the magnets 2407, maypropagate. It is appreciated that the ferromagnetic material used tobuild the ferromagnetic layer 2410 may, in certain embodiments, be anelectric insulator or a poorly conducting material such as Ferrite,Amorphous Ferrum, Kovar or Iron Powder, so as to reduce the generationof induced currents in the layer. This structure is operative to enhancethe magnetic field, by virtue of provision of a ferromagnetic material,rather than air, through which the principal magnetic field lines 2440pass as best seen in FIG. 5B. This structure is also operative toincrease the gradient of the magnetic field across the magnet thusachieving a stronger force for a given current across the coil Finally,this structure reduces cross-talk between adjacent magnets i.e. reducesthe influence that one magnet has on adjacent magnets by diminishing themagnetic field generated by each magnet at the locations occupied byother magnets.

It is appreciated that in certain embodiments, more than oneferromagnetic material layer and in some embodiments more than one coillayer may be provided, e.g. one on each side of the layer of movingelements.

Reference is now made to FIGS. 6-8 which illustrate examples of methodsfor using delay patterns for staggered activation of the movingelements, thereby to achieve a particular, synthetic, directivitypattern, such as an omni-directional (spherical), cylindrical,uni-directional (beam) or poly-directional (plurality of beams) pattern,which differs from the directivity pattern naturally produced by regularspeaker apparatuses being used to generate sound. This latterdirectivity pattern is referred to herein as the “natural” directivitypattern of the speaker apparatus. As described above, the naturaldirectivity pattern of speaker apparatus provided in accordance withcertain embodiments of the present invention typically depends on thegeometrical configuration of the array of moving elements. In theexample of FIG. 6, a synthetic directivity pattern comprising anomni-directional pattern with radius R_(img), is achieved using speakerapparatus whose natural directivity pattern comprises anomni-directional pattern with radius R_(true). In the example of FIGS.7A-7B, a synthetic directivity pattern comprising a cylindrical patternwith radius R_(img), is achieved using speaker apparatus whose naturaldirectivity pattern comprises a cylindrical pattern with radiusR_(true).

Specifically, FIG. 6 relates to an array 2500 having a spherical segmentconfiguration of radius R_(true) having a cross-sectional coverage angleα, that corresponds to a spherical coverage angle

$\left. {\Omega_{true} = {2\pi\;\sin^{2}\frac{\alpha}{4}\left( {2 - {\sin^{2}\frac{\alpha}{4}}} \right)}} \right).$To provide a synthetic spherical pattern having a radius R_(img) and across-sectional coverage angle

$\beta = {4\;{\arcsin\left( {\frac{R_{true}}{R_{img}}\sin\frac{\alpha}{4}} \right)}}$which corresponds to spherical coverage angle

$\left. {\Omega_{img} = {2\pi\;\sin^{2}\frac{\beta}{4}\left( {2 - {\sin^{2}\frac{\beta}{4}}} \right)}} \right),$a timing pattern may be used by the latching mechanism associated withthe array 2500, which introduces delays such that eachpressure-producing element (also termed herein “moving element”) 2510arrives at its, say, upper extreme position with a delay, as computedbelow, relative to an arbitrary temporal reference point. As shown, thedelay assigned to each pressure producing element 2510 typically dependson the distance r between that element and the axis of symmetry 2520 ofthe entire array 2500 of pressure producing elements. In particular, thedelay assigned to an individual pressure producing element whosedistance from the axis of symmetry is r, may be as follows:

${{delay} = \frac{\sqrt{\left( {R_{img} - R_{true} + \sqrt{R_{true}^{2} - r^{2}}} \right)^{2} + r^{2}}}{c}},$where r=distance between the symmetry axis passing the focal point P andthe individual pressure-producing element, c=the speed of sound throughthe medium in which the speaker is operating, radius R_(true) is thetrue (hardware) radius of the spherical surface, and R_(img) is theimaged radius of the synthetic spherical pattern.If R_(img)=R_(true), the required delay vs. r distribution is

${{delay} = \frac{\sqrt{\left( {R_{true} - R_{true} + \sqrt{R_{true}^{2} - r^{2}}} \right)^{2} + r^{2}}}{c}},{= {\frac{R_{true}}{c} = {const}}}$which means that no temporal staggering of the motion of the movingelements is required.

FIGS. 7A and 7B are cross-sectional and isometric illustrations,respectively, of an array having a cylindrical segment configuration ofradius R_(true), a cross-sectional coverage angle α, and an syntheticdirectivity pattern with cross-section coverage angle β. Typically, thelatching mechanism introduces a suitable (positive or zero) delay foreach individual pressure-producing element, using the formula:

${{delay} = \frac{\sqrt{\left( {R_{img} - R_{true} + \sqrt{R_{true}^{2} - r^{2}}} \right)^{2} + r^{2}}}{c}},$where r=distance between the symmetry plane and the individualpressure-producing element, c=the speed of sound through the medium inwhich the speaker is operating, radius R_(true) is the true (hardware)radius of the cylindrical surface and R_(img) is the imaged radius ofthe synthetic cylindrical surface. It is appreciated that if it isdesired to achieve R_(img)=R_(true), the required delay vs. rdistribution is

${{delay} = \frac{\sqrt{\left( {R_{true} - R_{true} + \sqrt{R_{true}^{2} - r^{2}}} \right)^{2} + r^{2}}}{c}},{= {\frac{R_{true}}{c} = {const}}}$which means that all moving elements may move synchronously. If theimaged coverage angle of the synthetic cylindrical pattern is β and thetrue coverage angle is α the imaged pattern radius is

$R_{img} = {R_{true}\frac{\sin\left( {\alpha/4} \right)}{\sin\left( {\beta/4} \right)}}$while the required delay vs. r distribution is not constant as evidentfrom the above delay equation.

Another example of using a particular array of moving elements having anatural directivity pattern, to achieve a synthetic pattern whichdiffers from the natural directivity pattern, is when an arraycomprising a portion of a spherical surface, defining a symmetry axis,is used to achieve a uni-directional directivity pattern directed inparallel to the symmetry axis. According to this embodiment, a suitabledelay (positive or zero) is introduced, via the latching mechanism, foreach individual pressure-producing element, using the formula:

${{delay} = \frac{R_{true} - \sqrt{R_{true}^{2} - r^{2}}}{c}},$where r=distance between the symmetry axis passing the focal point andthe individual pressure-producing element, c=the speed of sound throughthe medium in which the speaker is operating.

Yet another example of using a particular array of moving elementshaving a natural directivity pattern, to achieve a synthetic patternwhich differs from the natural directivity pattern, is when an arraycomprising a portion of a cylindrical surface defining a symmetry axis,is used to achieve a uni-directional directivity pattern directed inparallel to the symmetry axis and normally to the cylindrical surface.According to this embodiment, a suitable delay is provided for eachindividual one of the pressure-producing elements, using the formula:

${{delay} = \frac{R_{true} - \sqrt{R_{true}^{2} - r^{2}}}{c}},$where r=distance between the symmetry axis and the individualpressure-producing element, c=the speed of sound through the medium inwhich the speaker is operating.

More generally delay formulae for each of the moving elements, as afunction of the position of the moving element, may be as follows:

The following is a delay formula which may be employed when an array ofmoving elements of arbitrary configuration is used to obtain a syntheticspherical pattern:

${{delay} = \frac{r_{2}}{c}},$for each individual pressure producing element P2 at a distance r2 fromthe focal point O (the sphere center)The following is a delay formula which may be employed when an array ofmoving elements of arbitrary configuration is used to obtain a syntheticcylindrical pattern:

${{delay} = \frac{r_{1}}{c}},$for an individual pressure producing element P₂ at a distance r₁ fromthe focal line L (the cylinder axis).

The following is a delay formula which may be employed when an array ofmoving elements of arbitrary configuration is used to obtain a beam(planar wave) pattern:

${{delay} = \frac{r_{3}}{c}},$for an individual pressure producing element P₂ at a distance r₃ from aplane Σ which is parallel to the planar wave front (and normal to thewave propagation direction). FIG. 8 illustrates an arbitrary array ofpressure-generating elements to create any propagation pattern(spherical, cylindrical or planar/beam); each small square images apressure-producing element. Plane Σ is a selected one of the wave-frontsof a planar wave to be generated. The value r3 is the distance betweenplane Σ and a moving element location P3.

L is the focal line (the cylinder axis) of a cylindrical wave to begenerated within the brackets of implementations of the cylindricalpattern. The value r1 is the distance between this axis and a point P1at which a pressure-producing element is disposed. O is the focus (thesphere axis) of a cylindrical wave to be generated within the bracketsof implementations of the spherical pattern. The value r2 is thedistance between this center and any point P2 at which apressure-producing element is disposed.

Reference is now made to FIGS. 9A and 9B which are respective isometricand cross-sectional views of speaker apparatus constructed and operativein accordance with certain embodiments of the present invention andincluding an array 2700 of moving elements e.g. in accordance with anyof the embodiments shown and described herein, and a waveguide 2710associated therewith intended to change the directivity of soundproduced by the array 2700 of moving elements, e.g. because the geometryof the application mandates a particular orientation for the array,resulting in a natural directivity which does not happen to comply withthe requirements of the application. For example, in cellular telephonesit may be desired to provide a planar array arranged parallel to theflat front surface of the phone, however, it may be desired to provide abeam of sound emanating from the side of the phone. The particularwaveguide 2710 illustrated in FIGS. 9A-9B is intended to provide a beamof uni-directional sound directed in a direction indicated by arrow2720. As shown, the waveguide 2710 plane intersects array 2700 therebyto define a waveguide-array intersection axis 2730.

It is appreciated that the relatively small number of moving elements inthe apparatus of FIG. 9A is shown merely for simplicity; the array 2700may include any suitable number of moving elements such as thousands ofmoving elements.

Preferably, the array of moving elements includes latches associatedwith a latch controller as described in detail herein. However, in thisembodiment, the latch controller is operative to control at least onelatch so as to temporally staggering motion of individual movingelements thereby to achieve a desired directivity pattern, e.g. asindicated by arrow 2720 in the illustrated embodiment, by reducinginterference between moving elements. Typically, the latch controller isoperative to temporally stagger motion of individual moving elements inthe array such that individual moving elements move in order of theirrespective distances from the waveguide-array intersection. In theillustrated embodiment, the array of moving elements includes rows A, B,C, D, . . . which are increasingly distant from the intersection axis2730 and the latch controller may control the latches for each of theserows so as to introduce a delay Δt between adjacent rows, starting fromrow A and continuing until the row 2735 most distant from theintersection axis 2730 is reached (i.e. between rows A and B, B and C, Cand D, etc.). Delay Δt typically equals d/c where d is the distancebetween adjacent rows and c is the velocity of sound through the mediumin which the speaker is operating.

The waveguide may have a variety of configurations e.g. as shown inFIGS. 9B, 10A and 10B respectively. A particular advantage of theapparatus of FIG. 10A is that the main surface 2735 of the waveguide isparallel to the array 2700 thereby providing compactness.

According to one embodiment of the present invention, as shown in FIG.10C, the waveguide may itself comprise a pair of typically intersectingarrays 2700 and 2740 of moving elements 2750 which together serve awaveguide for the waves produced by both arrays 2700 and 2740. It isappreciated that the second array of moving elements 2740 need not beplanar as shown in FIG. 10C and may instead have any suitableconfiguration such as but not limited to those of the waveguides 2712and 2714 of FIGS. 10A and 10B respectively. Latch control for the secondarray may be the same, mutatis mutandis, as for the first array; thelatch controller may control the latches for each of rows A′, B′, C′, .. . of the second array 2740 so as to introduce a delay Δt betweenadjacent rows, starting from row A and continuing until the row mostdistant from the intersection axis 2760 is reached (i.e. between rows A′and B′, B′ and C′, C′ and D′, etc.).

The method of operation of FIG. 21 is generally suitable for speakersystems whose moving element arrays are in accordance with those shownand described in FIGS. 1-10C herein. When a waveguide is provided e.g.as described herein with reference to FIGS. 9A-10C, the LUT to be usedin step 3200 of FIG. 21 is typically constructed and operative to takethe presence of the waveguide into account. One suitable LUT is providedin FIG. 11, for an array which includes 20×20 moving elements. The LUTis used to determine an order of operation of the moving elements in thearray by assigning ordinal numbers to each moving element in the arrayas shown and selecting sets of moving elements to be operated inascending order of ordinal number. Specifically in the event that thelatch controller determines that N moving elements are to be moved froma first extreme latching position, e.g. the bottom position, to a secondextreme latching position, e.g. top position, the selected elements arethe N elements from among those currently in the bottom latchingposition whose respective ordinal numbers in the LUT are smallest.

In the event that the latch controller determines that M moving elementsare to be moved back from a second extreme latching position to thefirst extreme latching position, the selected elements are similarlythose M elements from among those currently in the second extremelatching position whose respective ordinal numbers in the LUT aresmallest.

More specifically, operating the array typically comprises liftingoperations (moving from the bottom latching position to the top latchingposition) and dropping operations (moving from the top latching positionto the bottom latching position). In a typical example, a sequence ofsets of moving elements, including N1, N2, N3 moving elementsrespectively as computed in step 3100 of FIG. 21, are lifted, followedby dropping operations of sets of M1, M2, M3 moving elements. In thisexample, assuming that the initial state of the array is such that allthe moving elements are in their bottom latching position, then N1+N2+N3must be equal or greater than M1+M2+M3 or else more elements are to bedropped than are at the top position after the lifting stages arefinished.

According to certain embodiments of the present invention, the first setof moving elements to be lifted includes those moving elements numbered1, N1, the second set includes those moving elements numbered N1+1, . .. N1+N2, the third set includes those moving elements N1+N2+1, . . . .N1+N2+N3. At the end of this stage, elements numbered 1 . . . N1+N2+N3are latched at the top latching position and the rest are latched at thebottom. The first dropping operation includes the set of moving elementsnumbered 1 . . . M1 (after which elements M1+1 . . . N1+N2+N3 are intheir top positions and the rest are in their bottom positions), thesecond set includes those moving elements numbered M1+1, . . . M1+M2,the third set includes those moving elements M1+M2+1, . . . M1+M2+M3. Atthe end of this stage, elements numbered 1 . . . M1+M2+M3 are latchedinto their bottom latching positions, elements M1+M2+M3+1 . . . N1+N2+N3are latched into their top positions and elements numbered N1+N2+N3+1and above are latched in their bottom positions.

As shown, generally, the LUT is constructed such that moving elementsclose to row A, the row closest to the intersection between waveguideand array, tend to be operated before moving elements which are furtherfrom row A. Also, at least for arrays of moving elements which arerelatively wide compared to the wavelength associated with the systemsampling rate, each set of moving elements selected for operation isselected so as to prefer moving elements close to a mid-axis 2800bisecting the rows A, B, C, . . . or A′, B′, C′ of FIGS. 10A-10C overmoving elements which are further from the mid-axis.

It is appreciated that the moving elements in such a set may, ifdisposed in different rows (e.g. A, B, C of FIGS. 10A-10C), operate notsynchronously but rather after delays corresponding to their respectivedistances from a row such as row A. If, for example, N moving elementscomprising a currently operating set are disposed at lines C, D and E,the distance between adjacent lines equals d, Δt=d/c (c being thevelocity of sound in the medium in which the speaker is disposed) andthe operation instruction is issued at time t, then the elements of rowsC, D and E may be caused to operate at times (t+2×Δt), (t+3×Δt) and(t+4×Δt) respectively. Only elements disposed at line A are caused tooperate immediately upon issuance of the operation instruction or, moreprecisely, as soon thereafter as the internal hardware and softwarelatency allows.

A method for building a LUT for a speaker which includes a waveguide isnow described. The method typically includes the following steps,performed in a suitable order such as the following:

Determine the wavelength of a sonic wave that has a frequency equal tothe sampling rate (clock) of the system, using:

$\lambda = \frac{f_{s}}{C}$where:λ—The wavelength [m]fs—Sampling rate [Hz]C—Velocity of sound [m/s]. For air at STD, C≈340 m/s

Define the primary axis of the array as the axis along which the soundpropagates. Determine whether the array is narrow or wide, and useeither the narrow array method or the wide array method below,accordingly. For example, a suitable criterion for making thisdetermination is that if the width, i.e. the dimension perpendicular tothe primary axis, i.e. the length of rows A, B, C, . . . , of the array,is equal or smaller than λ, the “narrow array” method describedhereafter may be used. Otherwise the “wide array” method may be used.

Assuming the array has N×M elements, where each column of the array(e.g. A,B,C,D of FIG. 9B) has N elements and there are M columns intotal, draw a LUT of M rows and N columns e.g. as shown in FIG. 11. Thefirst column (A) holds elements (1) . . . (N). The second column (B)elements are (N+1) . . . (2×N). The third (C) column elements are(2×N+1) . . . (3×N) etc. The last column holds elements [(M−1)×N+1] . .. (M×N). In general, the i^(th) column holds elements [(i−1)×N+1] . . .[i×N]. The order of the elements within each column is determined byeither the “narrow array” or “wide array” methods described below.

Narrow Array method: In narrow arrays, the ordering of the N elements ofeach column is believed to be of little importance. So, in certainembodiments random ordering may be used. In another embodiment“bit-reversal” order may be used. The following example shows“bit-reversal” ordering for a case wherein N equals 8 and M equals 10:Write number 0 . . . (N−1) in binary form:000001010011100101110111Reverse the order of the bits in each row:000100010110001101011111Convert back to decimal and add 1:15372648Copy and results to all the columns in the array. To the second columnadd 8. To the third column add 16. To the fourth column add 24 and so onand so forth. In general add (i−1)*8 to the i^(th) column as shown inFIG. 12A.Wide Array method: In one possible embodiment, the elements in eachcolumn are ordered according to their distance from the center of thecolumn (the cell closest to N/2). In the following example, N equals 8and M equals 10. The following steps may be performed, e.g. in thefollowing order:Write the number 1 in the 4th cell of the column. The rest of thenumbers 2 . . . 8 are written in ascending order on both sides of the4th cell, e.g. as shown in FIG. 12B. Copy and results to all the columnsin the array. To the second column add 8. To the third column add 16. Tothe fourth column add 24 and so on and so forth. In general add (i−1)*8to the ith column e.g. as shown in FIG. 12C.

The LUTs, and methods for constructed LUTs, shown and described herein,are suitable for performing step 3200 of FIG. 21 although they are notintended to be limiting. In the case of the embodiment of FIG. 10C, aseparate LUT is built for each of the two arrays shown (the first arrayhaving rows A, B, C and the second array having rows A′, B′, C′). TheLUT for the first array having rows A, B, C . . . may be as in FIG. 11or may be constructed using the methods shown and described above. TheLUT for the second array having rows A′, B′, C′, . . . is typically suchthat each moving element in the second array operates simultaneouslywith the moving element facing it in the first array. So, for example,moving element 2810′ may operate simultaneously with moving element2810, moving element 2820′ may operate simultaneously with movingelement 2820, and moving element 2830′ may operate simultaneously withmoving element 2830.

It is appreciated that the LUTs shown and described herein are only onepossible implementation of a pre-determined moving element selectioncriterion. Alternatively, any other suitable implementation of aparticular moving element selection criterion, such as but not limitedto those described herein or implied from the context of the LUTsdescribed herein may be employed, such as an algorithmic implementation.

According to certain embodiments of the present invention, andunexpectedly, the amplitude of the moving elements used in any of thesystems shown and described herein, may be much less, e.g. an order ofmagnitude less, than that predicted by conventional acoustic formulae.

Specifically, the conventional formula for computing pressure producedby a vibrating piston in an infinite baffle is:

$\begin{matrix}{P = \frac{\sqrt{2} \cdot \pi \cdot \rho \cdot S \cdot ɛ \cdot f_{s}^{2}}{2 \cdot R_{0}}} & (1)\end{matrix}$Where:P—The pressure produced by the piston [Pascal]ρ—The medium density (for air, p=1.2 at ATP) [KG/m3]S—The piston surface area [m2]∈—The motion amplitude (peak to peak) of the piston [m]f_(s)—The oscillation frequency [Hz]R₀—The distance from the source [m]If an array of moving elements, each including a piston, is provided,the total pressure produced equals to the sum of the pressures producedby all the elements. If they are all identical then the maximal pressureproducible by the array is:P _(T) =P·N  (2)Where:P_(T)—The total pressure produced by the array [Pascal]N—The number of elements in the arrayTypically, in the speaker apparatus shown and described herein, lessthan all the elements are working all the time. To compute the pressureproduced at a frequency different from the sampling rate, the followingequation may be used:

$\begin{matrix}{P_{f} = {P_{T} \cdot \frac{f}{f_{s}}}} & (3)\end{matrix}$To compute the SPL (Sound Pressure Level), the following formula may beused:

$\begin{matrix}{{SPL} = {20 \cdot {\log_{10}\left( \frac{P_{T}}{P_{0}} \right)}}} & (4)\end{matrix}$

Where:

SPL—The sound pressure level [dBSPL]

P₀—The reference 0 dB pressure [Pascal]—typically 20 μPa

Three examples of application-specific speakers are described herein.Example 1 employs the following parameters:

d—The moving element diameter is 450μ,

∈—The moving element peak-to-peak amplitude is 15μ,

f_(s)—The operating sampling frequency is 32000 Hz

f—The speaker is assumed to work in a telecom application where thebandwidth is 300 Hz-3.5 KHz. The SPL of the array of moving elementsincreases with frequency so if sufficient loudness is assured at thelowest frequency of interest, adequate SPL at the entire workingbandwidth is guaranteed. Hence, in this example f is 300 HzN—The number of elements in the array is 1000R₀—The reference distance is 1 mHence, the area of each element is:

$S = {{\pi \cdot \left( \frac{d}{2} \right)^{2}} = {{\pi \cdot \left( \frac{450 \cdot 10^{- 6}}{2} \right)^{2}} = {1.59 \cdot 10_{m^{2}}^{- 7}}}}$The pressure produced by each element is:

$\begin{matrix}{P = {\frac{\sqrt{2} \cdot \pi \cdot 1.2 \cdot 1.59 \cdot 10^{- 7} \cdot 150 \cdot 10^{- 6} \cdot 32000^{2}}{2 \cdot 1} = 0.065_{Pa}}} & (1)\end{matrix}$The total pressure of the array is therefore:P _(T)=0.065·1000=65_(Pa)  (2)The pressure produced at the lowest frequency of interest is therefore:

$\begin{matrix}{P_{f} = {{65 \cdot \frac{300}{32000}} = 0.61_{Pa}}} & (3)\end{matrix}$And the SPL is therefore:

$\begin{matrix}{{SPL} = {{20 \cdot {\log_{10}\left( \frac{0.61}{20 \cdot 10^{- 6}} \right)}} = 89.6_{{dB}_{SPL}}}} & (4)\end{matrix}$This matches the design criteria for this speaker which was 90 dB

An experiment was performed to investigate these parameter values.Moving elements with the following parameters were constructed:

d—The moving element diameter is 450μ

∈—The moving element peak-to-peak amplitude is 100μ

f_(s)—The operating sampling frequency is 32000 Hz

R₀—The reference distance is 1 m

The expected pressure of these elements was:

$\begin{matrix}{P = {\frac{\sqrt{2} \cdot \pi \cdot 1.2 \cdot 1.59 \cdot 10^{- 7} \cdot 100 \cdot 10^{- 6} \cdot 32000^{2}}{2 \cdot 1} = 0.043_{Pa}}} & (1)\end{matrix}$However, measurements of these elements in the course of the experimentindicated that in fact, they produced pressure levels of 0.4 Pa-0.5 Paor about 10 times the expected pressure. In view of the unexpectedlyincreased SPL, it was possible to reduce the amplitude to 10% of itsoriginal value or 10μ. Repeated measurements showed pressure levels of0.04 Pa-0.05 Pa which are suitable for the target application.

When a moving element and an electrode, provided in accordance withcertain embodiments of the present invention, are latched by applyingvoltage, termed herein “latching voltage”, therebetween, the latchingforce may gradually decrease e.g. due to charge trapping effects. Inorder to maintain effective latching, the latching voltage is typicallygradually increased over time so as to maintain a desired level oflatching force.

The electrode layer may be coated with a thin layer of dielectric(insulator), e.g Silicon Nitride or Sapphire. The negative pole of apower supply may be connected to the moving element and the positivepole to the electrode. Voltage is then applied to charge the twoelements. Typically, when the moving element and the electrode are inclose proximity, the strength of the electrostatic field between theirsurfaces is so strong it rips (ionizes) the molecules trapped in thesmall air gaps between those surfaces. The released electrons acceleratetowards the positive electrode. They hit the dielectric material atvelocities and energy levels sufficiently high such that some of thempenetrate and sink into the dielectric material. Due to thenon-conducting nature of the dielectric material, the penetratingelectrons become trapped in the dielectric, masking some of the positivecharge of the electrode with their own negative charge, thus reducingthe attracting latching force between the electrode and the movingelement. This process may be difficult to reverse as dielectrics, beinginsulators, do not allow electrons to travel freely through them. Thisproblem may be avoided by reversing the polarity of the applied voltagesuch that the positive pole is connected to the moving element and thenegative to the electrode. The accelerated electrons then impinge uponthe moving element and not the dielectric and since the moving elementis conductive (or coated with a conductor) the excess charge can beeasily dissipated and absorbed by the power supply.

It is appreciated that the dielectric layer may be applied to thesurface of the moving element rather than to that of the electrode, inwhich case the positive pole of the voltage is connected to theelectrode and the negative to the moving element.

There are also techniques known in the art that can overcome chargetrapping. One example is coating the dielectric layer with a thinconductive layer. This layer dissipates the charge applied by impactingelectrons. Since this conductor is in contact with the moving element,it short cuts the excess electrons to the moving element.

The technical field of the invention includes that of a digitaltransducer array of long-stroke electromechanical micro actuatorsconstructed using fabrication materials and techniques to produce lowcost devices for a wide variety of applications, such as audio speakers,biomedical dispensing applications, medical and industrial sensingsystems, optical switching, light reflection for display systems and anyother application that requires or can derive benefit from longer-travelactuation and/or the displacement of greater volumes of fluid e.g. airor liquid relative to the transducer size.

Certain embodiments of the present invention seeks to provide atransducer structure, a digital control mechanism and variousfabrication techniques to create transducer arrays with a number, N, ofmicro actuators. The array is typically constructed out of a structureof typically three primary layers which in certain embodiments wouldcomprise of a membrane layer fabricated out of a material of particularlow-fatigue properties that has typically been layered on both sideswith particular polar aligned magnetic coatings and etched with anumber, N, of unique “serpentine like” shapes, so as to enable portionsof the membrane bidirectional linear freedom of movement (the actuator).The bidirectional linear travel of each moving section of the membraneis confined within a chamber (actuator channels) naturally formedtypically by sandwiching the membrane layer between two mirror imagesupport structures constructed out of dielectric, Silicon, Polymer orany other like insulating substrate, are typically fabricated with Nprecisely sized through holes equal in number to the N serpentineetchings of the membrane and typically precisely positioned in a patternwhich precisely aligns each through hole with each serpentine etching ofthe membrane. Further affixed to the outer surfaces of both the top andbottom layers of the support structure are, typically, conductiveoverhanging surfaces such as conductive rings or discs (“addressableelectrodes”), which serve to attract and hold each actuator as itreaches its end of stroke typically by applying electrostatic charge.

A device constructed and operative in accordance with certainembodiments of the present invention is now described.

FIG. 14 is a perspective view of one suitable embodiment of the presentinvention.

FIG. 15 is an exploded view of a device constructed and operative inaccordance with certain embodiments of the present invention.

FIG. 16 is a simplified flowchart illustration of a suitable actuationmethod operative in accordance with certain embodiments of the presentinvention.

FIG. 17A is a block diagram of a speaker system constructed andoperative in accordance with certain embodiments of the presentinvention. FIG. 17B is a flow diagram of the speaker system constructedand operative in accordance with certain embodiments of the presentinvention. FIG. 18A illustrates a suitable relationship between thedifferent forces applied to the moving elements.

Whereas FIG. 14 illustrates an array of elements in a honeycombconstruction constructed and operative in accordance with certainembodiments of the present invention, FIG. 19 illustrates an apparatususing a plurality (array) of devices.

Effective addressing is typically achieved through unique patterns ofinterconnects between select electrodes and unique signal processingalgorithms which typically effectively segments the total number ofactuators in a single transducer, into N addressable actuator groups ofdifferent sizes, beginning with a group of one actuator followed by agroup of double the number of actuators of its previous group, until allN actuators in the transducer have been so grouped.

To attain actuator strokes the transducer is typically encompassed witha wire coil, which, when electrical current is applied, creates anelectromagnetic field across the entire transducer. The electromagneticfield causes the moving part of the membrane to move typically in alinear fashion through the actuator channels. If the current alternatesits polarity, it causes the moving part of the membrane to vibrate. Whenelectrostatic charge is applied to particular addressable electrodegroups, it will typically cause all actuators in that group to lock atthe end of the stroke, either on top or bottom of the support structurein accordance with the application requirement. Collectively thedisplacement provided by the transducer is achieved from the sum totalof the N actuators that are not locked at any particular interval (superposition).

The transducer construction is typically fully scalable in the number ofactuators per transducer, the size of each actuator, and the length ofstroke of each actuator, and the number of addressable actuator groups.In certain embodiments, the actuator elements may be constructed byetching various shapes into a particular material, or by using layeredmetallic disks that have been coated with a flexible material or byusing free floating actuator elements The membrane (flexure) materialsmay include Silicon, Beryllium Copper, Copper Tungsten alloys, CopperTitanium alloys, stainless steel or any other low fatigue material. Theaddressable electrodes of the support structure may be grouped in anypattern as to attain addressing as appropriate for the transducerapplication. The addressable electrodes may be affixed such that contactis created with the membrane actuator or in such a manner that there isno physical contact with the membrane. The substrate material may be ofany insulating material such as FR4, silicon, silicon dioxide, ceramicor any variety of plastics. In some embodiments the material may containferrite particles. The number of serpentine shapes etched into themembrane, or floating actuator elements may vary and the correspondingchannels of the support structure may be round, square or any othershape. The electromagnetic field may be created by winding a coil aroundthe entire transducer, around sections of the transducer or around eachactuator element or by placing one or more coils placed next to one ormore actuator elements.

In certain embodiments a direct digital method is used to produce soundusing an array of micro-speakers. Digital sound reconstruction typicallyinvolves the summation of discrete acoustic pulses of pressure toproduce sound-waves. These pulses may be based on a digital signalcoming from audio electronics or digital media in which each signal bitcontrols a group of micro-speakers.

In one suitable embodiment of the current invention, the n^(th) bit ofthe incoming digital signal controls 2^(n) micro-speakers in the array,where the most significant bit (MSB) controls about half of themicro-speakers and the least significant bit (LSB) controls at least asingle micro-speaker. When the signal for a particular bit is high, allof the speakers in the group assigned to the bit are typically activatedfor that sample interval. The number of speakers in the array and thepulse frequency determine the resolution of the resulting sound-wave. Ina typical embodiment, the pulse frequency may be the source-samplingrate. Through the post application of an acoustic low-pass filter fromthe human ear or other source, the listener typically hears anacoustically smoother signal identical to the original analog waveformrepresented by the digital signal.

According to the sound reconstruction method described herein, thegenerated sound pressure is proportional to the number of operatingspeakers. Different frequencies are produced by varying the number ofspeaker pulses over time. Unlike analog speakers, individualmicro-speakers typically operate in a non-linear region to maximizedynamic range while still being able to produce low frequency sounds.The net linearity of the array typically results from linearity of theacoustic wave equation and uniformity between individual speakers. Thetotal number of non-linear components in the generated sound wave istypically inversely related to the number of micro-speakers in thedevice.

In certain embodiments a digital transducer array is employed toimplement true, direct digital sound reconstruction. The producedsound's dynamic range is proportional to the number of micro-speakers inthe array. The maximal sound pressure is proportional to the stroke ofeach micro-speaker. It is therefore desirable to generate long stroketransducers and to use as many as possible. Several digital transducerarray devices have been developed over the years. One worth mentioningis a CMOS-MEMS micro-speaker developed at Carnegie Mellon University.Using CMOS fabrication process, they designed an 8-bit digital speakerchip with 255 square micro-speakers, each micro-speaker 216 μm on aside. The membrane is composed of a serpentine Al—SiO2 mesh coated withpolymer and can be electrostatically actuated by applying a varyingelectrical potential between the CMOS metal stack and silicon substrate.The resulting out of plane motion is the source of pressure waves thatproduce sound. Each membrane has a stroke of about 10 μm. Such shortstrokes are insufficient and the generated sound levels are too soft fora loudspeaker. Another issue is that the device requires a drivingvoltage of 40V. Such voltage requires complex and expensive switchingelectronics. Suitable embodiments of the device described hereinovercome some or all of these limitations and generate much louder soundlevels while eliminating the need for high switching voltages.

It is believed that the shape of each transducer has no significanteffect on the acoustic performance of the speaker. Transducers may bepacked in square, triangle or hexagonal grids, inter alia.

The current invention typically makes use of a combination of magneticand electrostatic forces to allow sufficiently long stroke whileavoiding the problems associated with traditional magnetic orelectrostatic actuators.

The moving elements of the transducer array are typically made toconduct electricity and may be magnetized so that the magnetic poles areperpendicular to the transducer array surface. Moderate conduction issufficient. A coil surrounds the entire transducer array or is placednext to each element and generates the actuation force. Applyingalternating current or alternating current pulses to the coil creates analternating magnetic field gradient that forces all the moving elementsto move up and down at the same frequency as the alternating current. Tocontrol each moving element, two electrodes may be employed, one aboveand one below the moving elements.

The current applied to the coil typically drives the moving elementsinto close proximity with the top and bottom electrode in turn. A smallelectrostatic charge is applied to the moving elements. Applying anopposite charge to one of the electrodes generates an attracting forcebetween the moving element and the electrode. When the moving element isvery close to the electrode, the attracting force typically becomeslarger than the force generated by the coil magnetic field and theretracting spring and the moving element is latched to the electrode.Removing the charge or some of it from the electrode typically allowsthe moving element to move along with all the other moving elements,under the influence of the coil magnetic field and the flexures.In accordance with certain embodiments, the actuator array may bemanufactured from 5 plates or layers:

-   -   Top electrode layer    -   Top spacers (together shown as layer 402)    -   Moving elements 403    -   Bottom spacers    -   Bottom electrode layer (together shown as layer 404)

In accordance with certain embodiments, the array is surrounded by alarge coil 401. The diameter of this coil is typically much larger thanthat of traditional coils used in prior art magnetic actuators. The coilcan be manufactured using conventional production methods.

In certain embodiments the moving element is made of a conductive andmagnetic material. Moderate electrical conduction is typicallysufficient. The moving element may be manufactured using many types ofmaterials, including but not limited to rubber, silicon, or metals andtheir alloys. If the material cannot be magnetized or a stronger magnetis desired, a magnet may be attached to it or it may be coated withmagnetic material. This coating is typically done by application, usinga screen printing process or other techniques known in the art, by epoxyor another resin loaded with magnetic powder. In some embodiments,screen printing can be performed using a resin mask created through aphoto-lithographic process. This layer is typically removed after curingthe resin/magnetic powder matrix. In certain embodiments the epoxy orresin is cured while the device is subjected to a strong magnetic field,orienting the powder particles in the resin matrix to the desireddirection. The geometry of the moving elements can vary. In yet otherembodiments, part of the moving elements may be coated with the magnetand cured with a magnetic field oriented in one direction while the restare coated later and cured in an opposite magnetic field causing theelements to move in opposite directions under the same external magneticfield. In one suitable embodiment, the moving element comprises a platethat has a serpentine shape surrounding it, typically cut out from thinfoil. Alternatively, in certain embodiments it is possible to use athick material thinned only in the flexure area or by bonding relativelythick plates to a thin layer patterned as flexures. This shape allowspart of the foil to move while the serpentine shape serves as acompliant flexure. In certain other embodiments, the moving part is acylinder or a sphere, free to move about between the top and bottomelectrodes.

Referring again to FIGS. 14 and 15, in certain embodiments a coil 304wrapped around the entire transducer array generates an electromagneticfield across the entire array structure, so that when current isapplied, the electromagnetic field causes the pistons 302 to move up anddown. FIG. 15 shows an exploded view of the device constructed andoperative in accordance with certain embodiments of the invention. Asshown, the exploded view of a transducer array structure reveals that ittypically comprises the following:

(a) A coil surrounding the entire transducer array 401 generates anelectromagnetic field across the entire array structure when voltage isapplied to it. One possible embodiment for the coil is described hereinwith reference to FIGS. 18B-18D.

(b) In certain embodiments a top layer construction 402 may comprise aspacer layer and electrode layer. In a certain embodiment this layer maycomprise a printed circuit board (herein after “PCB”) layer with anarray of accurately spaced cavities each typically having an electrodering affixed at the top of each cavity.

(c) The moving elements (“pistons”) 403 in the current embodiment may becomprised of a thin foil of conductive magnetized material cut or etchedwith many very accurate plates typically surrounded by “serpentine”shapes that serve as compliant flexures that impart the foils with aspecific measure of freedom of movement.

(d) A bottom layer construction 404 may comprise a spacer layer andelectrode layer. In a certain embodiment this layer may comprise adielectric layer with an array of accurately spaced cavities eachtypically having an electrode ring affixed at the bottom of each cavity.

Reference is again made to FIGS. 17A-17B. FIG. 17A shows a block diagramof the speaker system in accordance with certain embodiments of thepresent invention. In certain embodiments the digital input signal(common protocols are I2S, I2C or SPDIF) 801 enters into a logicprocessor 802 which in turn translates the signal to define the latchingmechanism of each grouping of moving elements. Group addressing istypically separated into two primary groups, one for latching the movingelements at the top, and one for latching the moving elements at thebottom of their strokes. Each group is typically then further separatedinto logical addressing groups typically starting with a group of atleast one moving element, followed by another group that doubles themoving elements of the previous group, followed by a another group whichagain doubles the number of elements of the previous, and so on, untilall moving elements of the entire array have been grouped. The Nth groupcomprises 2^(N-1) moving elements.

In the embodiment depicted in the block diagram of FIG. 17A, the topgroup of one element group 803, a two element group 804 and then a fourelement group 805 are shown and so on, until the total numbers of movingelements in the transducer array assembly have been addressed to receivea control signal from the processor 802.

The same grouping pattern is typically replicated for the bottomlatching mechanisms where a one element group 807 may be followed by atwo element group 808 and then a four element group 809 and so on, untilthe total numbers of moving elements in the transducer array assemblyhave been addressed to receive a control signal from the processor 802.

The processor 802 may also control an alternating current flow to thecoil that surrounds the entire transducer array 812, thus creating andcontrolling the magnetic field across the entire array. In certainembodiments a power amplifier 811 may be used to boost current to thecoil.

FIG. 17B illustrates a flow diagram of the speaker system. In certainembodiments where the sampling rate of the digital input signal 813might be different from the device natural sampling rate, the resamplingmodule 814 may re-sample the signal, so that it matches the device'ssampling-rate. Otherwise, the resampling module 814 passes the signalthrough as unmodified.

The scaling module 815 typically adds a bias level to the signal andscales it, assuming the incoming signal 813 resolution is M bits persample, and the sample values X range between −2^((M-1)) and2^((M-1))−1.

It is also assumed that in certain embodiments the speaker array has Nelement groups (numbered 1 . . . N), as described in FIG. 17A.

K is defined to be: K=N−M

Typically, if the input resolution is higher than the number of groupsin the speaker (M>N), K is negative and the input signal is scaled down.If the input resolution is lower than the number of groups in thespeaker (M<N), K is positive and the input signal is scaled up. If theyare equal, the input signal is not scaled, only biased. The output Y ofthe scaling module 815 may be: Y=2^(K)([X+2^(M-1)]. The output Y isrounded to the nearest integer. The value of Y now ranges between 0 and2N−1.

The bits comprising the binary value of Y are inspected. Each bitcontrols a different group of moving elements. The least significant bit(bit1) controls the smallest group (group 1). The next bit (bit2)controls a group twice as big (group 2). The next bit (bit3) controls agroup twice as big as group 2 etc. The most significant bit (bitN)controls the largest group (group N). The states of all the bitscomprising Y are typically inspected simultaneously by blocks 816, 823,. . . 824.

The bits are handled in a similar manner. Following is a suitable methodfor inspecting bit1:

Block 816 checks bit1 (least significant bit) of Y. If it is high, it iscompared to its previous state 817. If bit1 was high previously, thereis no need to change the position of the moving elements in group 1. Ifit was low before this, the processor waits for the magnetic field topoint upwards, as indicated by reference numeral 818 and then, asindicated by reference numeral 819, the processor typically releases thebottom latching mechanism B1, while engaging the top latching mechanismT1, allowing the moving elements in group 1 to move from the bottom tothe top of the device.If block 816 determines that bit1 of Y is low, it is compared to itsprevious state 820. If bit1 was low previously, there is no need tochange the position of the moving elements in group 1. If its previousstate was high, the processor waits for the magnetic field to pointdownwards, as indicated by reference numeral 821 and then, as indicatedby reference numeral 822, the processor releases the top latchingmechanism T1 while engaging the top latching mechanism B1, allowing themoving elements in group 1 to move from the top to the bottom of thedevice.

Referring again to FIG. 18A, typical relationships between the differentmajor forces applied to moving elements are shown. The different forcesbeing applied to the moving elements typically work in harmony tocounterbalance each other in order to achieve the desired function.Forces toward the center are shown as negative forces, while forcesdriving the element further away from the center (either toward the upor down latching mechanisms) are shown as positive forces.

In the present embodiment the moving element is influenced by 3 majorforces:

a. Magnetic force, created by the interaction of the magnetic field andthe hard magnet. The direction of this force depends on the polarity ofthe moving element magnet, the direction of the magnetic field and themagnetic field gradient.

b. Electrostatic force, typically created by applying a certain chargeto the electrode and an opposite charge to the moving element. Thedirection of this force is such as to attract the moving element to theelectrode (defined as positive in this figure). This force increasessignificantly when the distance between the moving element and theelectrode becomes very small, and/or where this gap comprises materialwith a high dielectric constant.c. Retracting force created by the flexures, (which act as springs). Thedirection of this force is always towards the center of the device(defined as negative in this figure). This force is relatively smallsince the flexures are compliant, and is linear in nature.

The relationship between the forces shows that typically, as the movingelement increasingly nears the end of its stroke, the electrostaticforce (generated by the latching mechanism) increases, ultimatelyachieving sufficient force to attract and latch the moving element. Whenthe latch is released, the retracting and magnetic forces are typicallyable to pull the moving element away from the latch toward the center,thereby inducing travel of the moving element. As the moving elementtravels to the center, typically, the retracting force of the flexurediminishes and ultimately is overcome, and is then controlled by theelectromagnetic force and the kinetic energy of the moving element.

FIG. 19 shows an apparatus including a plurality (array) of devices. Thestructure shows the use of plurality in certain embodiments of arraytransducers 1902 as to create a device 1901 capable of generating loudersound pressure levels or use beam-forming techniques (which extendbeyond the scope of this invention) to create directional sound waves.

The array may have any desired shape, and the round shapes in thedescription are only for illustrative purposes.

The device constructed and operative in accordance with one embodimentof the present invention and described above with reference to FIGS. 14,15, 17A-17B, and 19 inter alia, is now described both more generally,e.g. with reference to FIG. 13, and in further detail. Alternativeembodiments are also described. Referring now to FIG. 13 which is asimplified functional block diagram illustration of actuator apparatusfor generating a physical effect, it is appreciated that at least oneattribute of the physical effect corresponds to at least onecharacteristic of a digital input signal sampled periodically inaccordance with a clock. According to certain embodiments of the presentinvention, the apparatus of FIG. 13 comprises at least one actuatordevice, each actuating device including an array 10 of moving elementseach typically constrained to travel alternately back and forth along arespective axis in response to an alternating electromagnetic forceapplied to the array 10 of moving elements. Each moving element isconstructed and operative to be responsive to electromagnetic force.Each moving element may therefore comprise a conductor, may be formed ofa ferro magnetic material, may comprise a permanent magnet and maycomprise a current-bearing coil.

A latch 20 is operative to selectively latch at least one subset of themoving elements 10 in at least one latching position thereby to preventthe individual moving elements 10 from responding to the electromagneticforce. An electromagnetic field controller 30 is operative to receivethe clock and, accordingly, to control application of theelectromagnetic force by a magnetic field generator, 40, to the array ofmoving elements. A latch controller 50 is operative to receive thedigital input signal and to control the latch accordingly. The latchcontroller 50, in at least one mode of latch control operation, isoperative to set the number of moving elements 10 which oscillate freelyresponsive to the electromagnetic force applied by the magnetic fieldgenerator, e.g. coil 40 to be substantially proportional to theintensity of the sound, coded into the digital input signal it receives.Preferably, when the intensity of sound coded into the digital inputsignal is at a positive local maximum, all moving elements are latchedinto a first extreme position. When the intensity of sound coded intothe digital input signal is at a negative local maximum, all movingelements are latched into a second, opposing, extreme position.

Preferably, a physical effect, e.g. sound, resembling the input signalis achieved by matching the number of moving elements in an extremeposition e.g. a top position as described herein, to the digital samplevalue, typically after resampling and scaling as described in detailbelow. For example, if the digital sample value is currently 10, 10moving elements termed herein ME1, . . . ME10 may be in their toppositions. If the digital sample value then changes to 13, threeadditional moving elements termed herein ME11, ME12 and ME13 may beraised to their top position to reflect this. If the next sample valueis still 13, no moving elements need be put into motion to reflect this.If the digital sample value then changes to 16, 3 different movingelements (since ME11, ME12 and ME13 are already in their top positions),termed herein M14, M15 and M16, may be raised to their top positions toreflect this.

In some embodiments, as described in detail below, moving elements areconstructed and operative to be operated collectively in groups, such asa set of groups whose number of moving elements are all sequentialpowers of two, such as 31 moving elements constructed to be operated ingroups having 1, 2, 4, 8, 16 moving elements, respectively, each. Inthis case, and using the above example, when the sample value is, say,10, the two groups including 8 and 2 moving elements respectively areboth, say, up i.e. all moving elements in them are in their toppositions. When the sample value changes to 13, however, it is typicallyimpractical to directly shift 3 moving elements from their bottompositions to their top positions since in this example, due to thebinary grouping, this can only be done by raising the two groupsincluding 1 and 2 moving elements respectively, however, the groupincluding 2 moving elements, is already raised. But the number of toppixels may be otherwise matched to the sample value, 13: Since 13=8+4+1,the two groups including 4 and 1 pixels may be raised, and the groupincluding 2 pixels may be lowered, generating a net pressure change of+3, thereby to generate a sound resembling the input signal as desired,typically after resampling and scaling.

More generally, moving elements translated toward a first extremeposition such as upward generate pressure in a first direction termedherein positive pressure. Moving elements translated toward the oppositeextreme position such as downward generate pressure in the oppositedirection termed herein negative pressure. A certain amount of positiveor negative pressure may be obtained either by translating theappropriate number of moving elements in the corresponding direction, orby translating n moving elements in the corresponding direction andothers, m in number, in the opposite direction, such that the differencen-m corresponds to e.g. equals the sampled signal value, typically afterresampling and scaling.

The moving elements are typically formed of a material which is at leastmoderately electrically conductive such as silicon or silicon coated bya metal such as gold.

If the moving elements comprise permanent magnets, the permanent magnetsare typically magnetized during production such that the magnetic polesare co-linear to the desired axes of motion. A coil that typicallysurrounds the entire transducer array generates the actuation force. Tocontrol each moving element, two latch elements (typically comprisingelectro static latches or “electrodes”) are typically used, e.g. oneabove and one below the moving elements.

According to one embodiment, the actuator is a speaker and the array ofmoving elements 10 is disposed within a fluid medium. The controllers 30and 50 are then operative to define at least one attribute of the soundto correspond to at least one characteristic of the digital inputsignal. The sound has at least one wavelength thereby to define ashortest wavelength present in the sound and each moving element 10typically defines a cross section which is perpendicular to the movingelement's axis and which defines a largest dimension thereof, thelargest dimension of each cross-section typically being small relativeto, e.g. an order of magnitude smaller than, the shortest wavelength.

Referring again to FIGS. 14-15, FIG. 14 is an isometric view of a skewedarray of moving elements 10 each constrained to travel alternately backand forth along a respective axis in response to an alternatingelectromagnetic force applied to the array of moving elements 10 e.g. bya coil 40 wrapped around the array as shown. FIG. 15 is an exploded viewof a layered actuator device including an array of moving elements 403each constrained to travel alternately back and forth along a respectiveaxis in response to an alternating electromagnetic force applied to thearray of moving elements 403 by a coil 401, and a latch, formed as atleast one layer, operative to selectively latch at least one subset ofthe moving elements 403 in at least one latching position thereby toprevent the individual moving elements 403 from responding to theelectromagnetic force. Typically, the electromagnetic force is generatedusing a coil 401 that surrounds the array 403 as shown.

The latch typically comprises a pair of layers: a top latch layer 402and bottom latch layer 404 which, when charged, and when the movingelements are in an appropriate electromagnetic field as describedherein, latch the moving elements into top and bottom extreme positionsrespectively. Each of the latch layers 402 and 404 typically comprisesan electrode layer and spacer layer. The spacer layers 402 and 404 maygenerally be formed from any suitable dielectric material. Optionally,ferrite or ferro-magnetic particles may be added to the dielectricmaterial to decrease undesirable interaction between the magnets in themagnet layer.

FIG. 16 is a simplified flowchart illustration of a suitable actuationmethod operative in accordance with certain embodiments of the presentinvention. In FIG. 16, a physical effect is generated, at least oneattribute of which corresponds to at least one characteristic of adigital input signal sampled periodically in accordance with a systemclock signal. As shown, the method typically comprises (step 450)providing at least one array of moving elements 10 each constrained totravel alternately back and forth along an axis in response to analternating electromagnetic force applied to the array of movingelements 10 e.g. by magnetic field generator 40. In step 460, at leastone subset of the moving elements 10 is selectively latched in at leastone latching position by a latch 20 thereby to prevent the individualmoving elements 10 from responding to the electromagnetic force appliedby magnetic field generator 40. In step 470, the system clock signal isreceived and, accordingly, application of the electromagnetic force tothe array of moving elements is controlled. In step 480, the digitalinput signal is received, and the latching step 460 is controlledaccordingly. Typically, as described above, the latch 20 comprises apair of layers, each layer comprising an array of electrostatic latchelements and at least one space maintainer layer separates theelectrostatic latch layers and is formed of an insulating material.Typically, the latch and at least one space maintainer are manufacturedusing PCB production technology (FIG. 16, step 450). The array of movingelements typically comprises a magnetic layer 403 sandwiched between apair of electrode layers spaced from the magnetic layer by a pair ofdielectric spacer layers. Typically, at least one of the layers ismanufactured using wafer bonding technology, layer laminatingtechnology, and/or PCB production technology and/or combination of thesetechnologies (FIG. 16, step 455).

Referring again to FIGS. 17A-17B, FIG. 17A is a control diagramillustrating control of latch 20 by latch controller 50 of FIG. 13 andof the typically coil-induced electromagnetic force, by controller 30 ofFIG. 13, for a particular example in which the moving elements 10 arearranged in groups G1, G2, . . . GN that can each, selectably, beactuated collectively, wherein each latch in the latching layer istypically associated with a permanent magnet, and wherein the poles ofall of the permanent magnets in the latching layer are all identicallydisposed. The latch typically comprises, for each group or each movingelement in each group, a top latch and a bottom latch. The top andbottom latches for group Gk (k=1, . . . N) are termed Tk and Bkrespectively. In FIG. 17A the two controllers are both implemented inprocessor 802.

FIG. 17B is a flowchart illustrating a suitable method whereby latchingcontroller 50 of FIG. 13 may process an incoming input signal 801 andcontrol latches 20 of moving elements 10 accordingly, in groups. Theabbreviation “EM” indicates electromagnetic force applied upward ordownward, depending on the direction of the associated arrow, to arelevant group of moving elements. In the embodiment illustrated in FIG.17B, if at time t, the LSB of the re-scaled PCM signal is 1 (step 816),this indicates that the speaker elements in group G1 may be in theselected end-position. If (step 817) group G1 is already in the selectedend-position, no further action is required, however if the group G1 isnot yet in the selected end-position, the latching controller 50 waits(step 818) for the electromagnetic field to be upward and then (step819) releases the bottom latches in set B1 and engages the top latchesin set T1. This is also the case, mutatis mutandis, for all other groupsG2, . . . GN.

In FIG. 17B, the notation Tk or Bk followed by an upward pointing ordownward pointing arrow indicates latching or releasing (upward ordownward arrow respectively) of the top or bottom (T or B respectively)latch of the k'th group of moving elements.

FIG. 17C is a simplified functional block diagram illustration of aprocessor, such as the processor 802 of FIG. 17A, which is useful incontrolling substantially any of the actuator devices withelectro-static latch mechanisms shown and described herein. A singleprocessor, in the embodiment of FIG. 17C, implements bothelectromagnetic field controller 30 and latch controller 50. Theelectromagnetic field controller 30 typically receives the system clock805 which is typically a square wave and generates a sine wave with thesame frequency and phase, providing this to the coil 40 as an actuatingsignal. The DSP 810 may for example comprise a suitably programmed TI6000 digital signal processor commercially available from TexasInstruments. The program for the DSP 810 may reside in a suitable memorychip 820 such as a flash memory. The latch controller 50, in at leastone mode of latch control operation, is operative to set the number ofmoving elements which oscillate freely responsive to the electromagneticforce applied by the coil 40 to be substantially proportional to theintensity sound coded in the digital input signal.

The electromagnetic field controller 30 typically controls analternating current flow to the coil 40 that typically surrounds theentire array of moving elements 10, thus creating and controlling themagnetic field across the entire array. In certain embodiments a poweramplifier 811 may be used to boost current to the coil 40. Theelectromagnetic field controller 30 typically generates an alternatingelectromagnetic force whose alternation is synchronous with the systemclock 805.

The latch controller 50 is operative to receive the digital input signal801 and to control the latching mechanism 20 accordingly. Typically,each individual moving element 10 performs at most one transition perclock i.e. during one given clock, each moving element may move from itsbottom position to its top position, or move from its top position toits bottom position, or remain at one of either of those two positions.According to certain embodiments of the present invention, retention ofmoving elements 10 in their appropriate end positions is affected by thelatching controller 50.

Preferably, the latching controller 50 operates on the moving elementsin groups, termed herein “controlled groups”. All moving elements in anygiven group of moving elements are selectably either latched into theirtop positions, or into their bottom positions, or are unlatched.Preferably, the “controlled groups” form a sequence G1, G2, . . . andthe number of speaker elements in each controlled group Gk is aninteger, such as 2, to the power of (k−1), thereby allowing any desirednumber of speaker elements to be operated upon (latched upward, downwardor not at all) since any given number can be expressed as a sum ofpowers of, for example, two or ten or another suitable integer. If thetotal number of speaker elements is selected to be one less than anintegral power (N) of 2 such as 2047, it is possible to partition thetotal population of speaker elements into an integral number ofcontrolled groups namely N. For example, if there are 2047 speakerelements, the number of controlled groups in the sequence G1, G2, . . .is 11.

In this embodiment, since any individual value of the re-scaled PCMsignal can be represented as a sum of integral powers of 2, a suitablenumber of speaker elements can always be placed in the selectedend-position by collectively bringing all members of suitable controlledgroups into that end-position. For example, if at time t the value ofthe re-scaled PCM signal is 100, then since 100=64+32+4, groups G3, G6and G7 together include exactly 100 speaker elements and therefore, atthe time t, all members of these three groups are collectively broughtto the selected end position such as the “up” or “top” position and, atthe same time, all members of all groups other than these three groupsare collectively brought to the un-selected end position such as the“down” or “bottom” position. It is appreciated that each moving elementhas bottom and top latches, each typically generated by selectivelyapplying suitable local electrostatic forces, associated therewith tolatch it into its “down” and “up” positions respectively. The set ofbottom and top latches of the speaker elements in group Gk are termed Bkand Tk latches respectively.

FIG. 17D is a simplified flowchart illustration of a suitable method forinitializing the apparatus of FIGS. 13-17C. According to the method ofFIG. 17D, the array of moving elements 10 is put into initial motionincluding bringing each moving element 10 in the array of movingelements into at least one latching position. As described herein, bothtop and bottom latching positions are typically provided for each movingelement 10 in which case the step of bringing each moving element in thearray into at least one latching position typically comprises bringing afirst subset of the moving elements in the array into their top latchingpositions and a second subset, comprising all remaining elements in thearray, into their bottom latching positions. The first and secondsubsets are preferably selected such that when the moving elements inthe first and second subsets are in their top and bottom latchingpositions respectively, the total pressure produced by fluid such as airdisplaced by the moving elements 10 in the first subset is equal inmagnitude and opposite in direction to the total pressure produced byfluid such as air displaced by the moving elements in the second subset.

The moving elements 10 typically bear a charge having a predeterminedpolarity and each of the moving elements defines an individual naturalresonance frequency which tends to differ slightly from that of othermoving elements due to production tolerances, thereby to define anatural resonance frequency range, such as 42-46 KHz, for the array ofmoving elements. As described herein, typically, first and secondelectrostatic latching elements are provided which are operative tolatch the moving elements 10 into the top and bottom latching positionsrespectively and the step of putting the array of moving elements intomotion comprises (FIG. 17D):

Step 850: Charge the first (top or bottom) electrostatic latch of eachmoving element included in the first subset with a polarity opposite tothe pole, on the moving element, facing that latch. The first and secondsubsets may each comprise 50% of the total number of moving elements.

Step 855: Charge the second (bottom or top) electrostatic latch of eachmoving element included in the second subset with a polarity opposite tothe pole, on the moving element, facing that latch.

Step 860: As described above, the moving elements are designed to have acertain natural resonance frequency, f_(r). Design tools may includecomputer aided modeling tools such as finite elements analysis (FEA)software. In step 860, f_(CLK), the frequency of the system clock, whichdetermines the timing of the alternation of the electromagnetic field inwhich the moving elements are disposed, is set to the natural resonancefrequency of the moving element in the array which has the lowestnatural resonance frequency, referred to as f_(min) and typicallydetermined experimentally or by computer-aided modeling.

Steps 865-870: The system clock frequency may then be monotonicallyincreased, from an initial value of f_(min) to subsequent frequencyvalues separated by Δf until the system clock frequency has reached thenatural resonance frequency of the moving element in the array which hasthe highest natural resonance frequency, referred to as f_(max) andtypically determined experimentally or by computer-aided modeling. It isappreciated however that alternatively the system clock frequency mightbe monotonically decreased, from f_(max) to f_(min), or might be variednon-monotonically.

It is appreciated that when a moving element 10 is excited at itsnatural resonance frequency, f_(r), the moving element increases itsamplitude with every cycle, until reaching a certain maximal amplitudetermed hereinafter A_(max). Typically, the duration Δt required for themoving element to reach A_(max) is recorded during set-up and themagnetic force applied during the initialization sequence is selected tobe such that A_(max) is twice as large as the gap the moving elementneeds to travel from its idle state to either the top or bottom latch.

The Q factor or quality factor is a known factor which compares the timeconstant for decay of an oscillating physical system's amplitude to itsoscillation period. Equivalently, it compares the frequency at which asystem oscillates to the rate at which it dissipates its energy. Ahigher Q indicates a lower rate of energy dissipation relative to theoscillation frequency. Preferably, the Q factor of the moving elementsis determined either computationally or experimentally. The Q factor asdetermined describes how far removed the frequency f_(CLK) needs to befrom f_(r) (two possible values, one below f_(r) and one above f_(r))before the amplitude drops to 50% of A_(max). The difference between thetwo possible values is Δf.

As a result of the above steps, a sequence of electromagnetic forces ofalternating polarities is now applied to the array of moving elements.The time interval between consecutive applications of force of the samepolarity varies over time due to changes induced in the system clock,thereby to define a changing frequency level for the sequence. Thisresults in an increase, at any time t, of the amplitude of oscillationof all moving elements whose individual natural resonance frequency issufficiently similar to the frequency level at time t. The frequencylevel varies sufficiently slowly (i.e. only after a suitable intervalΔt, which may or may not be equal in all iterations) to enable the setS, of all moving elements whose natural resonance frequency is similarto the current frequency level, to be latched before the electromagneticfield alternation frequency level becomes so dissimilar to their naturalresonance frequency as to cease increasing the amplitude of oscillationof the set S of moving elements. The extent of variation of thefrequency level corresponds to the natural resonance frequency range.Typically, at the end of the initiation sequence (step 872), the systemclock f_(CLK) is set to the predefined system frequency, typically beingthe average or median natural resonance frequency of the moving elementsin the array, i.e. 44 KHz.

One method for determining the range of the natural resonancefrequencies of the moving elements is to examine the array of movingelements using a vibrometer and excite the array at differentfrequencies.

Referring again to FIGS. 18A-18D, FIG. 18A is a graph summarizing thevarious forces brought to bear on moving elements 10 in accordance withcertain embodiments of the present invention. FIG. 18B is a simplifiedpictorial illustration of a magnetic field gradient inducing layerconstructed and operative in accordance with certain embodiments of thepresent invention and comprising at least one winding conductive element2600 embedded in a dielectric substrate 2605 and typically configured towind between an array of channels 2610. Typically, there are no channels2610 along the perimeter of the conductive layer of FIG. 18B so that thegradient induced within channels adjacent the perimeter is substantiallythe same as the gradient induced in channels adjacent the center of theconductive layer.

If the layer of FIG. 18B is separate from the spacer layers describedabove, then the channels in the layer of FIG. 18B are disposed oppositeand as a continuation of the channels in the spacer layers described indetail above. The cross-sectional dimensions, e.g. diameters, ofchannels 2610 may be different than the diameters of the channels in thespacer layer. Alternatively, the layer of FIG. 18B may serve both as aspacer layer and as a magnetic field inducing layer in which case thechannels 2610 of FIG. 18B are exactly the spacer layer channelsdescribed hereinabove. It is appreciated that, for simplicity, theelectrodes forming part of the spacer layer are not shown in FIG. 18B.

FIGS. 18C and 18D illustrate the magnetic field gradient inductionfunction of the conductive layer of FIG. 18B. In FIG. 18C, the currentflowing through the winding element 2600 is indicated by arrows 2620.The direction of the resulting magnetic field is indicated by X's 2630and encircled dots 2640 in FIG. 18C, indicating locations at which theresulting magnetic field points into and out of the page, respectively.

Referring again to FIG. 19, an isometric array of actuators supportedwithin a support frame provide an active area which is the sum of theactive areas of the individual actuator arrays. In other words, in FIG.19, instead of a single one actuating device, a plurality of actuatingdevices is provided. The devices need not be identical and can each havedifferent characteristics such as but not limited to different clockfrequencies, different actuator element sizes and differentdisplacements. The devices may or may not share components such as butnot limited to coils 40 and/or magnetic field controllers 30 and/orlatch controller 50.

The term “active area” refers to the sum of cross-sectional areas of allactuator elements in each array. It is appreciated that generally, therange of sound volume (or, for a general actuator other than a speaker,the gain) which can be produced by a speaker constructed and operativein accordance with certain embodiments of the present invention is oftenlimited by the active area. Furthermore, the resolution of sound volumewhich can be produced is proportional to the number of actuator elementsprovided, which again is often limited by the active area. Typically,there is a practical limit to the size of each actuator array e.g. ifeach actuator array resides on a wafer.

If the speaker is to serve as a headphone, only a relatively small rangeof sound volume need be provided. Home speakers typically require anintermediate sound volume range whereas public address speakerstypically have a large sound volume range, e.g. their maximal volume maybe 120 dB. Speaker applications also differ in the amount of physicalspace available for the speaker. Finally, the resolution of sound volumefor a particular application is determined by the desired sound quality.e.g. cell phones typically do not require high sound quality, howeverspace is limited.

According to certain embodiments of the present invention, layers ofmagnets on the moving elements may be magnetized so as to be polarizedin directions other than the direction of movement of the element toachieve a maximum force along the electromagnetic field gradient alignedwith the desired element moving direction.

A particular feature of certain embodiments of the present invention isthat the stroke of motion performed by the moving elements is relativelylong because the field applied thereto is magnetic hence decays at arate which is inversely proportional to the distance between the movingelements and the current producing the magnetic field. In contrast, anelectrostatic field decays at a rate which is inversely proportional tothe square of the distance between the moving elements and the electriccharge producing the electrostatic field. As a result of the long strokeachieved by the moving elements, the velocity achieved thereby isincreased hence the loudness that can be achieved increases because theair pressure generated by the high velocity motion of the movingelements is increased.

It is appreciated that the embodiments specifically illustrated hereinare not intended to be limiting e.g. in the sense that the movingelements need not all be the same size, the groups of moving elements,or individual moving elements if actuated individually, need not operateat the same resonance nor with the same clock, and the moving elementsneed not have the same amplitude of displacement.

The speaker devices shown and described herein are typically operativeto generate a sound whose intensity corresponds to intensity valuescoded into an input digital signal. Any suitable protocol may beemployed to generate the input digital signal such as but not limited toPCM or PWM (SACD) protocols. Alternatively or in addition the device maysupport compressed digital protocols such as ADPCM, MP3, AAC, DTS, orAC3 in which case a decoder typically converts the compressed signalinto an uncompressed form such as PCM.

Design of digital loudspeakers in accordance with any of the embodimentsshown and described herein may be facilitated by application-specificcomputer modeling and simulations. Loudness computations may beperformed conventionally, e.g. using fluid dynamic finite-elementcomputer modeling and empiric experimentation.

Generally, as more speaker elements (moving elements) are provided, thedynamic range (difference between the loudest and softest volumes thatcan be produced) becomes wider, the distortion (the less the soundresembles the input signal) becomes smaller and the frequency rangebecomes wider. On the other hand, if less speaker elements are provided,the apparatus is smaller and less costly.

Generally, if the moving elements have large diameters, the ratiobetween active and inactive areas (the fill factor) improves, and thereis less stress on the flexures if any, assuming that the vibrationdisplacement remains the same, which translates into longer lifeexpectancy for the equipment. On the other hand, if the moving elementshave small diameters, more elements are provided per unit area, and dueto the lesser mass, less power is required to generate the desiredmovement. Generally, if the vibration displacement of the movingelements is large, more volume is produced by an array of a given size,whereas if the same quantity is small, there is less stress on theflexures, if any, and the power requirements are lower.

Generally, if the sample rate is high, the highest producible frequencyis high and the audible noise is reduced. On the other hand, if thesample rate is low, accelerations, forces, stress on flexures if any andpower requirements are lower.

Reference is now made to FIGS. 20A-20B which is are simplified generallyself-explanatory functional block diagram illustrations of suitablesystems for achieving a desired directivity pattern for a desired soundstream using a direct digital speaker such as any of those shown hereinin FIGS. 13-19 or such as a conventional direct digital speaker whichmay, for example comprise that shown and described in U.S. Pat. No.6,403,995 to David Thomas, assigned to Texas Instruments and issued 11Jun. 2002, or in Diamond Brett M., et al, “Digital sound reconstructionusing array of CMOS-MEMS micro-speakers”, Transducers '03, The 12^(th)International Conference on Solid State Sensors, Actuators andMicrosystems, Boston, Jun. 8-12, 2003.

If the direct digital speaker of FIG. 13 is used to achieve a desireddirectivity pattern for a desired sound stream, then typically, blocks3020, 3030 and 3040 in FIG. 20A comprise blocks 20, 30 and 40 of FIG. 13respectively and block 3050 comprises latch controller 50 of FIG. 13,programmed to implement the per-clock operation of block 3050 e.g. asshown and described herein with reference to FIG. 21.

FIG. 21 is a simplified flowchart illustration of per-clock operation ofthe moving element constraint controller 3050 of FIGS. 20A-20B, inaccordance with certain embodiments of the present invention.

Step 3100 determines how many moving elements should move during thecurrent clock. Typically, and as described in detail above withreference to FIGS. 13-19, the number of moving elements which are tomove during a given clock is generally proportional to the intensity ofthe input signal during that clock, suitably normalized e.g. asdescribed above with reference to resampler 814 and scaler 815 of FIG.17B.Step 3200 determines which moving elements should move during thecurrent clock, using, in some embodiments, a suitable moving elementselection LUT which is typically loaded into the memory of theconstraint controller 3050 of FIGS. 20A-20B during factory set-up. Eachsuch LUT is typically built for a specific moving element array takinginto account, inter alia, the array size and whether or not the array isskewed. Each directivity pattern which it is desired to achievetypically requires its own LUT.

Step 3300 determines the amount of delay with which to operate each ofthe moving elements of moving element array 3010 or 3012 of FIGS.20A-20B.

Step 3200 is now described in detail. A suitable method for performingstep 3200 is now described. Step 3200 typically employs a LUT (look uptable) which has cells which correspond one-to-one to the pressureproducing elements in the array. For example, if the array comprises arectangle of 100×200 pressure producing elements then the LUT may have100×200 cells. Each cell holds a uniquely appearing integer between 1and the total number of pressure producing elements such as 20000 in theillustrated example. Therefore, the LUT assigns an ordinal number toeach pressure producing element in the array. Associated in memory withthe LUT is a integer parameter P which stores an indication of thenumber of pressure producing elements currently in a first operativeconfiguration from among two operative configurations, characterized inthat transition of the pressure producing elements therebetween producespressure in the medium, such as air, in which the apparatus of theinvention is disposed. In some embodiments, pressure in oppositedirections is obtained when the elements move from the firstconfiguration to the second, as opposed to when the elements move fromthe second configuration to the first. In other embodiments, pressure isobtained as long as the elements are in the first configuration, and nopressure is obtained when the elements are in the second configuration.

Typically, P is initialized during set-up as described below, and isthen assigned a current value in each clock by step 3100. In theimmediately following step 3200 in the same clock, P pressure producingelements are brought to their first operative configuration and N-Ppressure producing elements are brought to their second operativeconfiguration where N is the number of pressure producing elements inthe array. The P elements selected to be in their first operativeconfiguration are those whose ordinal number as determined by the LUT issmaller than P. The N-P elements selected to be in their secondoperative configuration are those whose ordinal number as determined bythe LUT is greater than or equal to P.

One of these configurations, say the first, is typically arbitrarilyconsidered the “positive” configuration whereas the other configuration,say the second, is then considered the “negative” configuration.Alternatively, in some applications there may be a physical reason toselect a specific one of the configurations to be the positiveconfiguration. The pressure generated when a pressure producing elementmoves from the second configuration to this first configuration istermed “positive pressure” whereas the pressure generated when apressure producing element moves from the second configuration to thisfirst configuration is termed “positive pressure”. The pressuregenerated by a single transition from one configuration to the other istermed herein a pressure “pulse”.

During set-up, the parameter P is typically given an initial value equalto half of the number of pressure producing elements in the array suchas 10000 in the present example. The array is then initialized such thateach pressure producing element whose ordinal number as determined bythe LUT is less than P is brought to its first configuration and theremaining pressure producing elements are brought to their secondconfiguration.

A suitable LUT (look up table), which has cells which correspondone-to-one to the N pressure producing elements in the array, storingintegers from 1 to N, may be generated as follows:

A criterion for LUT quality is first determined, which may beapplication-specific. One suitable criterion for LUT quality is nowdescribed.

A list is prepared of all possible subsets of consecutive integersranging between 1 and N. In the present example, the first subset,termed hereinafter S2₁, includes 2 integers: 1 and 2; the second subset,S2₂ includes the integers 2 and 3, and so on for all subsets containingtwo integers. The last two-element subset, S2₁₉₉₉₉, contains theintegers 19999 and 20000. The list also includes all possible threeelement subsets, namely, to continue the example, S3₁ (which includesintegers 1, 2, 3), S3₂ (which includes integers 2, 3, 4), . . . S3₁₉₉₉₈(which includes integers 19998, 19999, 20000). The list also includesall 4 element subsets, 5 element subsets and so on and so forth. Thelast subset, S20000₁ contains all 20000 elements. In general, a subsetcontaining K integers, starting at i is labeled SK_(i). It isappreciated that for a LUT containing N cells, the number of possiblesubsets M equals M=(N−1)*N/2.

For each subset SK_(i), a set of coordinates is defined (X_(i), Y_(i)),(X_(i+1), Y_(i+1)), . . . (X_(i+K-1), Y_(i+K-1)) such that thecoordinates represent the position of the pressure-producing elementswhose ordinal numbers are i, i+1, i+k−1 according to the current LUT.

For each subset SK_(i), a propagation angle θK_(i) is computed e.g.using analytic or numeric computation methods, typically using suitablecomputer simulation applications such as Matlab, MatCAD or Mathematica.The sound waves' propagation angles are computed for K coherent soundsources, disposed at positions (X_(i), Y_(i)), (X_(i+1), Y_(i+1)), . . .(X_(i+K-1), Y_(i+K-1)), all producing sinusoidal waves at the same phaseand at a frequency equal to the system sampling rate, e.g. 44100 Hz.

A “propagation angle of a subset” is defined as follows: Each subsetcorresponds to a subset of pressure producing elements. A reference axisis defined passing through the center of mass of the array of pressureproducing elements and perpendicular to its main surface. The intensityof sound generated by the subset of pressure producing elementsapproaches a maximum as one retreats from the array of pressureproducing elements along the reference axis. Therefore, a maximalintensity for the subset may be defined by measuring the intensity at alocation L which is on the reference axis and sufficiently distant fromthe array so as to ensure that the differences between the distance oflocation L and each of the pressure producing elements in the subset aresufficiently, e.g. an order of a magnitude, smaller than the wavelengthλ associated with the system clock. At least one reference plane isdefined which includes the reference axis. It is appreciated that aninfinite number of such reference planes exists. For cylindricalpropagation applications in which a focal axis is defined, select areference plane which includes the focal axis. It is appreciated that aLUT constructed on this basis would typically also be suitable foromnidirectional applications. For propagation applications in which afocal point is defined as described herein, select a reference planewhich includes the focal point. If more than one such reference planeexists, select two such reference planes which are mutuallyperpendicular.

The propagation angle of the subset, termed herein θK_(i), is definedfor each reference plane selected for that subset, as follows: Define animaginary circle within the reference plane whose center is at the pointof intersection between the reference axis and the main surface of thearray and whose radius is the distance between L and the main surface ofthe array. Select two locations on the circumference of the circle onboth sides of the reference axis respectively, in which the soundintensity generated by the subset of pressure producing elements is halfof the maximal intensity measured at L. The angle defined between tworadii connecting the center of the circle to these two locationsrespectively is termed the propagation angle of the subset for thatreference plane. If the subset has two perpendicular reference planes asdescribed above, simple or weighted average of the two propagationangles may be computed to obtain a single propagation angle θK_(i) forthe subset. If the directivity pattern across a certain reference plane,e.g. a vertical plane, is more important than that across the other,perpendicular reference plane, greater weight is assigned to the moreimportant plane. For example, in certain applications the most importantconsideration may be to prevent unwanted noise from reaching locationson different floors in which case a vertical reference plane would bemore heavily weighted than the horizontal reference plane. An example ofa suitable criterion for the “best-ness” of a specific LUT is:LUT_(score)=1/[(average of all θK_(i))×(standard deviation of allθK_(i))]

To determine the most suitable LUT, one may use a computer simulation totest and score all possible permutations i.e. all possible N-cell LUTs,and selecting the best one thereof.

It is appreciated that the number of LUTs, each containing N cells, isN! (N factorial). If N is sufficiently large, it becomes impractical totest and evaluate all possible LUTs i.e. all possible permutations ofintegers into LUT cells. If such is the case, a smaller number of LUTpermutations may be selected, e.g. randomly, and the best one thereof isselected.

It is appreciated that alternatively, step 3200 may be performed withoutresort to a fixed LUT stored during set-up. Instead, the set ofP_(t)-P_(t-1) pressure producing elements to be activated may beselected by selecting the best subset of P_(t)-P_(t-1) elements fromamong the set of pressure producing elements which are currently in thesecond operative configuration. This may be done by estimating thepropagation angle θ for each possible subset of P_(t)-P_(t-1) elementsand selecting that subset which best matches the desired propagationpattern.

P_(t) refers to the current value of P whereas P_(t-1) refers to thevalue of P in the previous system clock.

Furthermore, it is appreciated that in those applications in which thedirectivity pattern is not important, any set of pressure producingelements may be employed to achieve a temporal pressure pattern dictatedby the input signal.

Step 3300, in which the amount of delay with which to operate each ofthe moving elements of moving element array 3010 or 3012 of FIGS.20A-20B, is computed, determines the directionality of the soundgenerated by the speaker. Suitable methods and formulae for optionallypositioning the moving element array as a function of desireddirectionality of propagation, if possible, and for computing delaysalso as a function of desired directionality of propagation, are nowdescribed, for three example propagation patterns termed hereinomni-directional, cylindrical and uni-directional. It is appreciatedthat the three propagation patterns discussed particularly herewithinare discussed merely by way of example.

FIGS. 22A-22B, taken together, describe a simplified example of asolution for performing step 3300 when it is desired to achieveomni-directional sound i.e. sound which propagates outward through threedimensional space from a given point location termed herein the “focalpoint” of the omni-directional sound. Specifically, FIG. 22A is asimplified diagram of an omni-directional propagation pattern having afocal point 3400 and FIG. 22B is a diagram of a suitable positioning ofa moving element array relative to the focal point of the desiredomni-directional sound propagation pattern of FIG. 22A. In theillustrated embodiment, the array of moving elements referencedgenerally 3010 or 3012 in FIGS. 20A-20B comprises, merely by way ofexample, a typically non-skewed array 3410 of 14×21 moving elements. Asshown, the array of moving elements is preferably although notnecessarily positioned, as illustrated in FIG. 22B, such that itsgeometric center (located between the 7^(th) and 8^(th) rows, at the11^(th) column) of the array of moving elements coincides with the focalpoint 3400 of the omni-directional pattern, located at the center of theconcentric circles representing the omni-directional pattern as shown inFIG. 22A. The center of the array may also be positioned at theprojection of the focal point of the omni-directional pattern onto theplane of the moving element array 3410. It is appreciated that the arrayneed not be positioned as illustrated and may instead be positioned atany suitable location, such as a fixed location independent of theparticular propagation pattern currently selected by a user.

It is appreciated that the array need not be of the specified dimensionsor shape. In fact suitable embodiments of direct digital speakers arecomprised of thousands to hundreds of thousands of pressure-producingelements. The shape of the array may change according to applicationand/or use.

It is also appreciated that the focal point referred to herein need notbe positioned on the main surface defined by the array ofpressure-producing elements. Changing the distance between the focalpoint and the main surface of the array of the pressure-producingelements changes the directionality pattern of the device. e.g. placingthe focal point on the surface (zero distance) would produce trueomni-directional directivity pattern where sounds intensity remainessentially equal regardless of the angle in which the sound propagates.Placing the focal point at a certain distance, d behind the surface ofpressure-producing elements defines a projection cone (in the case of around array) or a projection pyramid (in the case of a square orrectangular array) that is characterized by a head angle narrower than180 degrees. Placing the focal point at an infinite distance behind themain surface of the pressure producing elements (given that the soundproduced by the pressure producing elements is produced in front of themain surface) typically defines a projection cone or a projectionpyramid that is very narrow and would produce a true unidirectionaldirectivity pattern. Typically, the sound intensity throughout theprojection cone or projection pyramid remains essentially equal whilethe intensity outside the cone or pyramid is significantly lower. It isappreciated that d may be either 0 or infinity in certain applications.In certain applications, d may be determined as a function of a usercontrol.

Referring back to FIG. 22A, each circle shown represents half a phaseand has a radius r which is computed using the following formula:r=(Ndλ/2+N ^(2λ/)4)^(0.5)where: N=the serial number of the circle, counting outward from thecenter and starting from 1,d=the distance of the plane of the non-skewed array from the focal pointof the omni-directional soundλ=c T, where c=the speed of sound through the medium in which thespeaker is operating, typically air, and T=the period of the systemclock of FIG. 20A or 20B (not shown).

It is appreciated that specific delay values for the moving elements inarray 3410, suitable for achieving the omni-directional pattern of FIG.22A, may be determined as follows:

(a) Any moving element which coincides with a circle whose serial numberis N is assigned a delay value of N T/2.

(b) Any moving element which does not coincide with a circle, andinstead falls between a pair of circles whose serial numbers are N andN+1 is assigned a delay value by interpolating e.g. linearly between thefollowing two values: NT/2 and (N+1)T/2.

Alternatively, a suitable formula for determining delays is described indetail below.

The scope of the present invention includes but is not limited to amethod for controlling direct digital speaker apparatus receiving adigital input signal and generating sound accordingly, the methodcomprising providing an array of pressure-producing elements, andcomputing a timing pattern determining if and when eachpressure-producing element is operative to produce pressure pulses so asto achieve a desired directivity pattern. The array is then operated inaccordance with the timing pattern in order to achieve sound having thedesired directivity pattern.

Optionally, the providing and computing steps are performed a pluralityof times thereby to obtain a corresponding plurality of arrays and acorresponding plurality of timing patterns defining a correspondingplurality of directivity patterns. The method then also comprises thestep of operating the plurality of arrays simultaneously in accordancewith the corresponding plurality of timing patterns respectively therebyto obtain a single directivity pattern comprising a combination of thedirectivity patterns corresponding to the plurality of timing patterns.The plurality of arrays may in fact comprise portions of a single largerarray. So, for example, a single array of pressure producing elementssuch as any of those shown and described herein may be partitioned intoregions, e.g. quarters, and the pressure producing elements in eachregion may be operated in accordance with its own particular timingpattern or delay pattern. For example, this allows a pattern of several,say four, different unidirectional beams to be achieved. Alternatively,to give another example, this allows, say, omni-directional backgroundsound to be superimposed on one or more different foreground soundstreams each respectively having its own, say, uni-directional,cylindrical or omni-directional propagation pattern. It is appreciatedthat in multi-directional embodiments, each of the unidirectional beamsmay produce a different digital input signal, e.g. the left and rightchannels of a stereophonic signal.

It is appreciated that the electromagnetic field controller 30 ispreferably designed to ensure that the alternating current flowingthrough the coil maintains appropriate magnetic field strength at alltimes and under all conditions so as to allow sufficient proximitybetween the moving elements 10 and the electrostatic latches 20 toenable latching, while preventing the moving elements 10 from moving toofast and damaging themselves or the latches 20 as a result of impact.

In some applications, a small displacement (typically up to 5 microns)of translating elements is sufficient for appropriate operation. In suchspeakers, the electromagnetic driving coil may be eliminated. In thiscase set-up may be affected by the same electrodes which are designed tofunction as latching elements. This is possible because in short stroketranslating elements, the electrostatic forces between flexures andelectrode elements, even in the initial flexure position in whichmaximal air gaps occur, are sufficient to swing the flexures underresonance conditions.

FIG. 23A is an isometric view of small-stroke translating elementapparatus as described above. FIG. 23B is an exploded view of theapparatus of FIG. 23A. FIG. 23C is an enlarged illustration of thebubble of FIG. 23A. A flexure 4030 is interposed between two rigidelectrodes 4010 and 4050 which are separated from flexure 4030 byinsulator layers 4020 and 4040. To provide appropriate operation, theelectrodes comprise an array of through-holes 4055 providing sufficientair passing through, to generate sound as required by the application.

As shown, the apparatus is a short stroke apparatus in which the stroke,typically determined by the thickness of the insulating layers 4020 and4040, falls within the operative range of the electrostatic forcegenerated by the voltage applied between the electrodes 4010 and 4050and the translating element layer 4030. In particular, the apparatus ofFIGS. 23A-23C is constructed such that the electrostatic force iscapable of inducing translation of the translating elements whereverthey may be located rather than only when the translating elements havebeen previously caused to approach the relevant electrode. As is wellknown, one characteristic of an insulator (and of air) is the “breakdownvoltage” of each which defines the maximum voltage difference that canbe applied across the material before the insulator collapses andconducts. Therefore, the voltage that can be applied between thetranslating element layer 4030 and the electrode layers 4010 and 4050 islimited by the breakdown voltage of the insulating layers 4020 and 4040and surrounding air. Consequently, the stroke is selected to be smallenough to allow the limited voltage that can be applied to inducetranslation of the translating elements 4030 irrespective of theirlocation.

Suitable voltages to be applied to the electrodes in these translatingelements, when the apparatus is in start procedure and in normaloperation mode, are now described. In start procedure, as shown in FIG.24A, two electrodes operate synchronously at resonance frequencies whichare mutually shifted by half a period. As shown in FIG. 24B, aperiodical voltage is applied to each electrode which may vary from zeroup to a maximal level. Optionally, zero or essentially zero voltage maybe maintained for half the period.

Responsive to a “position translation” command issued by a suitablecontroller at time t_0, the latching electrode 4010 is shorted to theflexure for a short time (the “release” period on the top graph of FIG.24C) and then reverts to a low “idle” voltage. About half way throughthis idle period, as shown in the bottom graph in FIG. 24B, electrode4050 is connected to a high voltage for a short duration, which durationis also termed herein the “catching” duration. The first electrode 4010then transmits to a latching voltage to provide latching.

Instead of shorting the latching electrode 4010 to the flexure duringthe “release” period, it may be desirable to apply a voltage, typicallylower than the voltage during the “hold” period, between the flexure andthe latching electrode 4010, perhaps even one of opposite polarity, thusexpediting dissipation of charge from the latching electrode 4010.

According to certain embodiments of the present invention, a suitableelectronic circuit may be provided to transfer the charge from theelectrode to a suitable charge storage device (e.g. a capacitor) ratherthan disposing of the charge. The stored charge may be reused at a laterstage rather than generating a new charge, thus improving the electricalefficiency of the system.

Also, instead of storing the charge in a charge storing device, it maybe desirable to transfer the charge from the “release” stage electrodeto a different latching electrode that may be at a “catch” stage at thetime, e.g. the latching electrode 4050 disposed at the latching positionopposite to the one from which the charge is removed.

The top graph of FIG. 24A is a graph of displacement of the resilientlytranslating elements 4030 of FIGS. 23A, -23B vs. time. The middle graphof FIG. 24A is a graph of the voltage, versus time, between the flexureand first electrode 4010. The bottom graph of FIG. 24A is a graph of thevoltage, versus time, between the flexure and second electrode layers4050.

In normal operation mode, as shown in FIG. 24A, initially thetranslating element is latched to the latching electrode 4010 by arelatively low latching voltage (latching voltage) such as 10-20% of themaximal voltage (top graph). The other electrode 4050 (bottom graph) maybe kept under a rather low voltage (idle level).

Following receipt of an “up-down translation” command from a suitablecontroller, a very low “release” voltage is typically applied to thefirst latching electrode for a short time, typically 10% to 60% of theperiod. The first latching electrode may even be shortened to thetranslating element layer 4030. This voltage then increases to an “idle”level typically comprising about 30-40% of the maximal voltage. Inparallel the voltage at the second electrode, initially at idle level,jumps up to a maximal “catch” level for a very short time, about half aperiod after initiation of the release voltage on the first electrode.After the “catch” plateau, the voltage at the second electrode thendecreases to a relatively low latching voltage as shown. Followingreceipt of an “up-down translation” command from a suitable controller,the sequence is just the opposite of that described above as occurringfollowing receipt of a “down-up translation” command: A very low“release” voltage is applied to the second electrode for a short time,typically for 10% to 60% of the period. The voltage at the secondelectrode then increases to an “idle” level which is typically about30-40% of the maximal voltage. In parallel the voltage at the firstelectrode, maintained at an idle level, jumps up to a maximal “catch”level for a very short time about half a period after the releaseoccurs, and subsequently decreases down to a relatively low latchingvoltage.

As shown, typically the up-down translation time interval and thedown-up translation time interval are equal in length. The up-downtranslation typically terminates well before T time has elapsed(counting from receipt of the up down translation command), typically atclose to 0.5T, such as approximately 0.53-0.55T, from receipt of the updown translation command. The same is true, mutatis mutandis, for thedown-up translation.

It is appreciated that the graphs of FIGS. 24A and 24B inter alia aresimplifications, e.g. because the start procedure typically comprises upto several hundred pulses of voltage and not only a few as shown. Anysuitable number of pulses can be provided in the start procedure,assuming that the number of pulses is capable of bringing thetranslating elements into their extreme positions. The number of pulsesmay be determined, inter alia, based upon some or all of the maximalvoltage level, stroke length, and acoustic impedance of the translatingelement. Generally, the higher the voltage level the less pulses need beemployed; the larger the stroke the greater number of pulses need beemployed; and the higher the acoustic impedance the more pulses need beemployed. As an example, for a translating element having a 400 umdiameter circular active surface, each translating element distanced 2μm from its electrode (i.e. having a 2 um stroke) and a voltage level of120 V, a few dozen pulses, e.g. approximately 20 pulses, might beemployed.

The “roof” of each pulse during the start procedure need not be flat asin FIG. 24A nor need it incline upward and then downward specificallylinearly as shown for simplicity in FIG. 24B.

FIG. 25 is a simplified pictorial diagram of actuator apparatus havingonly one latch to latch its translating elements, the apparatus beingconstructed and operative in accordance with certain embodiments of thepresent invention. In FIG. 25 each translating element comprises onlyone latching electrode 4450 such that flexure 4230 may be latched intoonly a single “latched” position 4335. When released, flexure 4430 movesback and forth as indicated by arrow 4440 arriving at the oppositeextreme position 4245 without latching. To provide the same acousticeffect as in previous embodiments, two identical subsets of translatingelements may be provided which operate synchronously and in accordancewith a common algorithm. Suitable velocity and displacement vs. timesequences for the two subsets and total pressure effect for the twosubsets of translating elements respectively are illustrated in FIGS.26-27.

Prior to the translation command all translating elements are latched intheir single latching positions 4335. Upon receiving a “translateforward” command in time 4331, translating elements in the first subsetare released whereas release of translating elements in the secondsubset lags, relatively, by half a period (one clock). After theirrespective releases from time 4332, both subsets move harmonicallybetween their extreme positions without latching. Upon receiving a“translate back” command in time 4370, translating elements belonging tothe subset which at that moment is close to the latching position, arelatched. FIG. 26 illustrates a situation when the first subset is aboutto be latched whereas FIG. 27 illustrates a situation when the secondsubset is about to be latched. In FIG. 26, once translating elements inthe first subset are latched, translating elements in the second subsetare latched after a half period (one clock) lag at time-point 4371. InFIG. 27 once translating elements in the second subset are latched,translating elements in the first subset are latched after a half period(one clock) lag at time-point 4371. After their respective latches, bothsubsets remain static until a new “translate forward” command has beenreceived.

Curves 4342 and 4344 represent the displacements of the first and secondsubsets of translating elements respectively. Curves 4352 and 4354represent the velocities (pressures) of the first and second subsets oftranslating elements respectively. As a result, at a time clock betweenpoints 4331 and 4332 a positive total pressure pulse 4351 is formed; ata time clock between points 4370 and 4371 a negative total pressurepulse 4371 is formed; and between time points 4332 and 4370 a zero (ni)total pressure effect is obtained.

FIGS. 28A and 28B are isometric views of example embodiments of actuatorapparatus designed to operate with only one latch. In FIG. 28Athrough-holes are provided in the electrode whereas in FIG. 28B theholes are in the membrane. FIGS. 29A and 29B are exploded views of thedevices of FIGS. 28A and 28B respectively. The driving force in theseembodiments need not be electrostatic, and may be of any other type suchas but not limited to an electromagnetic force, or a combination ofelectrostatic and electromagnetic forces. The actuator apparatus of FIG.28 typically comprises a flexure 4030 and an electrode 4050 separatedfrom flexure 4430 by an insulation layer 4040 as shown.

EXAMPLE

FIG. 30 is a diagram of an array of translating elements to be used, inpairs, to generate a sound. It is appreciated that the array of FIG. 30,for simplicity, is shown as including only a relatively small number ofelements such as 24 elements yielding 12 pairs of elements. In practice,quality of sound considerations usually demands that the array includesmany more pairs of elements such as one or more thousands of elements.

FIG. 31 is a pressure vs. time graph for a sound to be generated usingthe array of FIG. 30 and using a scheme in which the controllerselectably latches (or not) all of the translating elements in the arrayinto a single extreme position e.g. the first extreme position.

FIG. 32 is a composite graph including graphs of translations of each ofthe elements in the array of FIG. 30, as a function of time, whichtranslations can yield the sound depicted in FIG. 31.

It is appreciated that in the example of FIGS. 30-32, each twotranslating elements are permanently paired together. For example,element 1-1 in the above example is always paired with element 1-2.However, in certain applications, it may be desired to have afluctuating pairing system including even a random pairing system, inwhich element 1-1 (say) may be paired initially with element 1-2 butsubsequently with other elements e.g. as a result of an on-the-flydecision as to the current capabilities of various adjacent translatingelements.

Operation according to certain embodiments of the present invention isdescribed by way of example, for actuator apparatus including 24translating elements arranged in a 5×5 matrix whose central element ismissing as shown in FIG. 30. The 24 active translating elements 1-1, . .. 3-2 and 3-4, . . . 5-5 are partitioned into the following 12cooperating pairs: (1-1,2-1), (1-2,2-2), (1-3,1-4), (1-5,2-5),(2-3,2-4), (3-1,3-2), (3-4,3-5), (4-1,4-2), (4-3,4-4), (4-5, 5-5),(5-1,5-2), (5-3,5-4). It is appreciated that alternatively, any otherpairs might have been defined.

FIG. 31 is a graph of a sound pressure wave to be created using theactuator apparatus of FIG. 30. The sound pressure wave to be created, asinusoidal wave with a period equal to 12 time clocks, may beapproximated by 12 pressure pulses distributed through the 12 timeclocks respectively.

FIG. 32 is a composite graph of the respective displacements of thetranslating elements 1-1, . . . 3-2 and 3-4, . . . 5-5 of FIG. 30 which,in combination, provide the total pressure effect shown in the top graphof FIG. 32. In the specific example shown, elements (1-1,2-1) are usedto create pulses 1 and 7 in the total pressure effect. At the beginningof time clock “1” translating element 1-1 is released and starts tooscillate; after one clock translating element 2-1 (which has been“assigned” to be the cooperating element for element 1-1) is releasedand starts to oscillate simultaneously with translating element 1-1. Atthe beginning of time clock “7” translating element 1-1 is latched andafter one clock translating element 2-1 is latched.

In order to create pulses 2 and 8 which are double the height of pulses1 and 7 respectively, 2 pairs of cooperating translating elements(1-2,2-2) and (1-3,1-4) are used. At the beginning of time clock “2”translating elements 1-2 and 1-3 are released and start to oscillate;after one clock the cooperating translating elements 2-2 and 1-4 arereleased and start to oscillate simultaneously with translating elements1-2 and 1-3 respectively. At the beginning of time clock “8” translatingelements 1-2 and 1-3 are latched and after one clock the translatingelements 2-2 and 2-4 are latched. Pulse pairs 3 and 9, 4 and 10, 5 and11, and 6 and 12, are created similarly.

Built-in fuses may be added to the flexure design irrespective ofwhether the embodiment of FIGS. 24A-24B is employed or not. Such fusesallow any translating element which has suffered a breakdown to bedisconnected immediately. If group operation of certain translatingelements is provided, a particular advantage of fuse provision is thatappropriate operation of the remaining translating elements belonging tothe same group, all of which are typically connected to one another inparallel, is maintained despite breakdowns.

Reference is now made to FIG. 33 which is a top-view illustration of animproved speaker apparatus flexure layer characterized in thattranslating element flexures 4011 are surrounded by a non-closed narrowgap 4013 so as to form a narrow isthmus 4014 conducting a chargingcurrent. In the event of a fault in the insulating layer separating thetranslating element and any one of its respective electrodes, resultingin insulation breakdown and short circuit to an electrode to which aworking voltage has been applied, shorting current flows through isthmus4014 and burns it out, disconnecting the problematic translating elementand affording appropriate operation of the remaining translatingelements in the same group.

The dimensions (width, length and/or thickness) of the isthmus 4014 maybe selected such that under normal operating conditions, in which nobreakdown of the insulating layer has occurred, the charging currentflowing through the isthmus 4014 is substantially (e.g. an order ofmagnitude) smaller than the current required to burn the isthmus,whereas the breakdown current flowing through the isthmus 4014 in caseof insulation fault is substantially (e.g. an order of magnitude) largerthan the current required to assure burning of the isthmus 4014.

It is appreciated that the term “stroke” is used herein to refer to halfof the peak-to-peak distance defined by a translating element.

It is appreciated that the term “adjacent” refers to translatingelements whose distance from one another is small relative to thewavelength of sound generated by the elastic translation of any one ofthe elements. Therefore, “adjacent elements” may comprise, but do notnecessarily comprise, neighboring elements in the array. Typically, theadjacent translating elements are as near as possible to one another.The distance between the adjacent translating elements may for example,depending on the application, be 1 to 10 percent of the wavelength ofsound generated by the elastic translation of any one of the elements.

It is appreciated that sound as used herein refers to vibrationtransmitted through a solid, liquid, or gas such as but not limited tothose vibrations whose frequencies are capable of being detected byhuman ears.

It is appreciated that the latching device typically includes several ormany latches each of which provide the two operative states eitherindividually for a single translating element or collectively for asubset of the totality of elastically translating elements in the array.According to one embodiment of the present invention, one individuallatch may latch its corresponding translating element or elements intothe first position, whereas another individual latch may latch itscorresponding translating element or elements into the second position.It may even be the case, that the latches for the first and secondelements in an individual pair, include a first latch latching the firstelement into the first extreme position and a second latch which latchesthe second element into the second extreme position. Alternatively, thelatch/es for the first and second elements in an individual pair,include one or two latches latching both of the first and secondelements into the same one of the two extreme positions e.g. the firstextreme position. According to another embodiment of the presentinvention, all of the latches latch their respective correspondingtranslating element or elements into the same one of the two extremepositions e.g. the first extreme position.

With specific reference to the Figures, it is stressed that theparticulars shown are by way of example and for purposes of illustrativediscussion of the suitable embodiments of the present invention only,and are presented in the cause of providing what is believed to be themost useful and readily understood description of the principles andconceptual aspects of the invention. In this regard, no attempt is madeto show structural details of the invention in more detail than isnecessary for a fundamental understanding of the invention. Thedescription taken with the drawings makes apparent to those skilled inthe art how the several forms of the invention may be embodied inpractice.

Features of the present invention which are described in the context ofseparate embodiments may also be provided in combination in a singleembodiment. Conversely, features of the invention which are describedfor brevity in the context of a single embodiment may be providedseparately or in any suitable subcombination. For example, movingelements may be free floating, or may be mounted on filament-likeflexures or may have a surrounding portion formed of a flexiblematerial. Independently of this, the apparatus may or may not beconfigured to reduce air leakage therethrough as described above.Independently of all this, the moving element may for example comprise aconductor, coil, ring- or disc-shaped permanent magnet, or ring- ordisc-shaped ferromagnet and the magnets, if provided, may or may not bearranged such that the poles of some e.g. 50% thereof are oppositelydisposed to the poles of the remaining e.g. 50% of the magnets.

Independently of all this, the latch shape may, in cross-section, besolid, annular, perforated with or without a large central portion, ornotched or have any other suitable configuration. Independently of allthis, control of latches may be individual or by groups or anycombination thereof. Independently of all this, there may be one or morearrays of actuator elements which each may or may not be skewed and thecross-section of each actuator element may be circular, square,triangular, hexagonal or any other suitable shape.

It is appreciated that software components of the present inventionincluding programs and data may, if desired, be implemented in ROM (readonly memory) form including CD-ROMs, EPROMs and EEPROMs, or may bestored in any other suitable computer-readable medium such as but notlimited to disks of various kinds, cards of various kinds and RAMs.Components described herein as software may, alternatively, beimplemented wholly or partly in hardware, if desired, using conventionaltechniques.

The present invention also includes computer program products,comprising a computer usable medium having a computer readable programcode embodied therein, the computer readable program code adapted to beexecuted to implement any or all of the methods shown and describedherein.

The present invention has been described with a certain degree ofparticularity, but those versed in the art will readily appreciate thatvarious alterations and modifications may be carried out to include thescope of the following Claims:

The invention claimed is:
 1. An actuator array for generating sound, theactuator array comprising at least one actuator device, the at least oneactuator device including: (a) a latching electrode; (b) a flexurecomprising one or more flexible elements peripheral to and integrallyformed with a central portion, the central portion being configured totravel back and forth along a respective axis perpendicular to thelatching electrode in response to an electrostatic force generable byapplying a voltage between the latching electrode and the flexure; (c)an insulation layer separating the latching electrode from the flexure.2. The actuator array according to claim 1, wherein the latchingelectrode is designed to function as an electrostatic latching elementby being oppositely charged such that the latching electrode and thecentral portion of the at least one actuator device constitute a pair ofoppositely charged electrodes.
 3. The actuator array according to claim1, further comprising a controller configured for applying voltagesbetween the latching electrode and the flexure so as to control drivingand latching of the central portion of the at least one actuator device.4. The actuator array according to claim 3 being configured to receive adigital input signal and wherein the controller is configured to controlthe driving and the latching of the central portion of the at least oneactuator device so as to generate a sound at least one attribute ofwhich corresponds to at least one characteristic of the digital inputsignal.
 5. The actuator array according to claim 1, wherein the latchingelectrode comprises partial annular openings facing the peripheralflexible elements of the flexure.
 6. The actuator array according toclaim 1, wherein the latching electrode further comprises arrays ofthrough holes.
 7. The actuator array according to claim 6, wherein thearrays of through holes face the central portion of the flexure.
 8. Anactuation system for generating sound, the system comprising: a latchingelectrode; at least one array of translating elements each constrainedto travel alternately back and forth from the latching electrode alongan axis perpendicular to said latching electrode, in response toactivation of electrostatic forces; and a controller operative to usesaid electrostatic forces to selectably latch at least one subset ofsaid translating elements with the latching electrode.
 9. The actuationsystem according to claim 8 wherein said electrostatic forces on eachindividual translating element are generated by at least one voltageapplied between the individual translating element and the latchingelectrode.